Polymeric membrane compositions

ABSTRACT

Blends of very low density polyethylene produced using metallocene catalysts (mVLDPE) and polypropylene are disclosed. The polymer blends include a metallocene-catalyzed VLDPE polymer having a density of less than 0.916 g/cm 3 , the mVLDPE polymer preferably being linear and without long chain branching, a polypropylene homopolymer, random copolymer, or impact copolymer, and optionally flame retardant additives. The polymer blends are particularly suitable in membrane applications where increased tear resistance and tensile strength are desirable, such as in roof membranes, geomembranes, and pond liners.

1. FIELD OF THE INVENTION

[0001] The present invention relates generally to polymer blendssuitable for use in roofing applications. More specifically, the presentinvention is directed to blends of very low density polyethyleneproduced using metallocene catalysts, and polypropylene homopolymers orcopolymers, and membranes such as roofing membranes, geomembranes andpond liners formed of such blends.

2. BACKGROUND

[0002] Thermoplastic polyolefins (“TPO”) are widely used in membraneapplications. In roofing applications in particular, the use ofTPO-based membranes is rapidly growing. Most TPO roofing membranesinclude a fabric or scrim coated on both sides with polymer compoundsbased on polypropylene reactor copolymers. The top layer, which is oftenwhite, is formulated with non-halogen flame-retardants (predominantlymagnesium hydroxide), UV stabilizers, antioxidants and pigments(titanium di-oxide). The bottom layer is generally polymer-rich. Thewhite top layer reflects sunlight and prevents thermal heating insidethe building, thereby reducing air conditioning costs. Ability toformulate white compounds is an advantage for TPO over some otherroofing systems. TPO membranes are heat welded directly on the roof toform large sheets. This process eliminates the need for expensivesolvent-based adhesives that are commonly used in other single-plyroofing. Because of the widespread use of TPO membranes in roofing andother applications under environmentally harsh conditions, it isparticularly desirable to improve membrane properties, such as strengthand tear resistance.

[0003] Blends of metallocene catalyzed plastomers with polypropylene inmembrane applications are known. For example, EXACT™ 0201 and EXACT™8201 (metallocene-catalyzed ethylene-octene plastomers having densitiesof 0.902 g/cm³ and 0.882 g/cm³, respectively, available from ExxonMobilChemical Co., Houston, Tex.) have been used in blends with apolypropylene impact copolymer to form membranes suitable for roofingapplications. (N. Dharmarajan, T. C. Yu and D. K. Metzler, “MetallocenePlastomer Based Thermoplastic Olefin Compounds for Roof MembraneApplications”, Society of Plastics Engineers (SPE) ANTEC 2001 Meeting,May 2001, Dallas, Tex.) The plastomer-polypropylene compositions aresaid to have a good balance of mechanical properties, notably tensilestrength and tear resistance, as well as other desirable properties.

[0004] Other background references include WO 92/14784; WO 98/54260;Patent Abstracts of Japan, vol. 2000, no. 05 (2000-09-14) & JP 2000063581 (2000-02-29); Patent Abstracts of Japan, vol. 1996, no. 02(1996-02-29) & JP 07 278377A (1995-10-24); EP 0 850 756; PatentAbstracts of Japan, vol. 1997, no. 03 (1997-03-31) & JP 08 311271A(1996-11-26); and U.S. Pat. No. 5,006,383.

[0005] It would be desirable to have polymer blend compositions suitablefor membrane applications, wherein the membrane would have furtherimproved tensile strength and tear resistance. Improved tensile strengthand tear resistance would provide superior wind uplift resistance to theolefin membrane (resistance to high velocity winds) and the potential todowngauge to reduce composite thickness. It would further be desirableto provide polymer blend compositions suitable for membraneapplications, wherein the compositions can be formulated at lower cost,without sacrificing ultimate membrane properties.

3. SUMMARY

[0006] In one embodiment, the present invention is directed to amembrane, such as a pond liner, a geomembrane or a roofing membrane,formed of a polymer blend. The blend includes a metallocene-catalyzedvery low density polyethylene (mVLDPE) polymer having a density of from0.906 g/cm³ or greater to 0.915 g/cm³ or less, and a polypropylene (PP)component. The mVLDPE and PP components are present in the blendcomposition in a weight ratio of from 9:1 to 1:9, or from 9:1 to 1:1.

[0007] In another embodiment, the present invention is directed to amembrane, such as but not limited to a roofing membrane, pond liner orgeomembrane, formed of a polymer blend. The blend includes ametallocene-catalyzed very low density polyethylene (mVLDPE) polymerhaving a density of from 0.906 to 0.915 g/cm³, and a polypropylene (PP)component including at least one of a polypropylene homopolymer and apolypropylene/ethylene copolymer having a polymerized ethylene contentof from 0.5 to 40 wt. %. The mVLDPE and PP components are present in theblend composition in a weight ratio of from 9:1 to 1:9, or from 9:1 to1:1.

[0008] In another embodiment, the present invention is directed to acomposite membrane having first and second layers formed of themVLDPE/PP blends described herein, and an intermediate polymericreinforcing layer of, for example, polyester or polypropylene fabric.

[0009] In other embodiments, the present invention is directed to any ofthe membranes and composite membranes described above, wherein themetallocene-catalyzed VLDPE polymer (mVLDPE) is produced using anunbridged biscyclopentadienyl metallocene catalyst system.

[0010] In other embodiments, the present invention is directed to any ofthe membranes and composite membranes described above, wherein themVLDPE polymer is a copolymer of ethylene and at least one C₃-C₂₀alpha-olefin, and has at least one of: (i) a comonomer content of from 5to 15 wt. %; (ii) a composition distribution breadth index of from 50%to 85%; (iii) a molecular weight distribution Mw/Mn of from 2 to 3; (iv)a molecular weight distribution Mz/Mw of less than 2; and (v) a bimodalcomposition distribution.

4. DETAILED DESCRIPTION 4.1 The mVLDPE Component

[0011] The polymer blends and membranes of the present invention includea metallocene catalyzed very low density polyethylene (mVLDPE) polymer.As used herein, the terms “very low density polyethylene” polymer and“VLDPE” polymer refer to a polyethylene copolymer having a density ofless than 0.916 g/cm³. As used herein, the term “polyethylene copolymer”indicates a polymer formed of more than 50 mol % polymerized ethyleneunits, and the remaining less than 50 mol % polymerized units beingpolymerized α-olefin comonomers, such as C₃-C₂₀ α-olefins or C₃-C₁₂α-olefins. The α-olefin comonomer can be linear or branched, and two ormore comonomers can be used, if desired. Examples of suitable comonomersinclude linear C₃-C₁₂ α-olefins, and α-olefins having one or more C₁-C₃alkyl branches, or an aryl group. Specific examples include propylene;1-butene, 3-methyl-1-butene; 3,3-dimethyl-1-butene; 1-pentene; 1-pentenewith one or more methyl, ethyl or propyl substituents; 1-hexene with oneor more methyl, ethyl or propyl substituents; 1-heptene with one or moremethyl, ethyl or propyl substituents; 1-octene with one or more methyl,ethyl or propyl substituents; 1-nonene with one or more methyl, ethyl orpropyl substituents; ethyl, methyl or dimethyl-substituted 1-decene;1-dodecene; and styrene. It should be appreciated that the list ofcomonomers above is merely exemplary, and is not intended to belimiting. Preferred comonomers include propylene, 1-butene, 1-pentene,4-methyl-1-pentene, 1-hexene, 1-octene and styrene, more preferably1-butene, 1-hexene, and 1-octene.

[0012] Although not generally preferred, other useful comonomers includepolar vinyl, conjugated and non-conjugated dienes, acetylene andaldehyde monomers, which can be included in minor amounts in terpolymercompositions. Non-conjugated dienes useful as co-monomers preferably arestraight chain, hydrocarbon di-olefins or cycloalkenyl-substitutedalkenes, having 6 to 15 carbon atoms. Suitable non-conjugated dienesinclude, for example: (a) straight chain acyclic dienes, such as1,4-hexadiene and 1,6-octadiene; (b) branched chain acyclic dienes, suchas 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene; and3,7-dimethyl-1,7-octadiene; (c) single ring alicyclic dienes, such as1,4-cyclohexadiene; 1,5-cyclo-octadiene and 1,7-cyclododecadiene; (d)multi-ring alicyclic fused and bridged ring dienes, such astetrahydroindene; norbomadiene; methyl-tetrahydroindene;dicyclopentadiene (DCPD); bicyclo-(2.2.1)-hepta-2,5-diene; alkenyl,alkylidene, cycloalkenyl and cycloalkylidene norbornenes, such as5-methylene-2-norbornene (MNB), 5-propenyl-2-norbornene,5-isopropylidene-2-norbornene, 5-(4-cyclopentenyl)-2-norbornene,5-cyclohexylidene-2-norbornene, and 5-vinyl-2-norbornene (VNB); and (e)cycloalkenyl-substituted alkenes, such as vinyl cyclohexene, allylcyclohexene, vinyl cyclooctene, 4-vinyl cyclohexene, allyl cyclodecene,and vinyl cyclododecene. Of the non-conjugated dienes typically used,the preferred dienes are dicyclopentadiene, 1,4-hexadiene,5-methylene-2-norbornene, 5-ethylidene-2-norbornene, andtetracyclo-(Δ-11,12)-5,8-dodecene. Particularly preferred diolefins are5-ethylidene-2-norbornene (ENB), 1,4-hexadiene, dicyclopentadiene(DCPD), norbornadiene, and 5-vinyl-2-norbornene (VNB). Note thatthroughout this description the terms “non-conjugated diene” and “diene”are used interchangeably.

[0013] It should be appreciated that the amount of comonomer used willdepend upon the desired density of the mVLDPE polymer and the specificcomonomers selected. For one embodiment of the mVLDPE polymer comprisingan ethylene/butene copolymer, the molar ratio of butene to ethyleneshould be from about 0.015 to 0.035, preferably from 0.020 to 0.030. Forone embodiment of the mVLDPE polymer comprising an ethylene/hexenecopolymer, the molar ratio of hexene to ethylene should be from about0.015 to 0.035, preferably from 0.020 to 0.030. For one embodiment ofthe mVLDPE polymer comprising an ethylene/octene copolymer, the molarratio of octene to ethylene should be from about 0.015 to 0.035,preferably from 0.020 to 0.030. In general, the comonomer may be presentin an amount of 25% or less by weight, preferably 20% or less by weightand more preferably 15% or less by weight. In one embodiment, thecomonomer may be present in an amount of 5% or more by weight. It iswell-understood in the art that, for a given comonomer, the density ofthe mVLDPE polymer produced therefrom decreases as the comonomer contentincreases. One skilled in the art can readily determine the appropriatecomonomer content appropriate to produce a VLDPE polymer having adesired density.

[0014] The mVLDPE polymer has a density of less than 0.916 g/cm³, andpreferably greater than 0.905 g/cm³. Thus, a preferred density range forthe mVLDPE polymer is 0.906 g/cm³ to 0.915 g/cm³. Alternate lower limitsof the mVLDPE polymer density include 0.908 g/cm³ or 0.910 g/cm³.Alternative upper limits of the mVLDPE polymer include 0.912 g/cm³ or0.914 g/cm³. Use of higher density ethylene copolymers, such as LLDPEshaving a density of at least 0.916 g/cm³, would result in membraneshaving an undesirable increased stiffness, leading to flexibilityproblems in flexible membrane applications.

[0015] The mVLDPE polymer is further characterized by a melt index (MI)of from 0.5 to 20 g/10 min (dg/min), as measured in accordance withASTM-1238 condition E (I_(2.16), 190° C.). In one or more specificembodiments, alternative lower limits for the melt index include 0.7 and1.0 g/10 min, and alternative upper limits for the melt index include 5,10, 12 and 15 g/10 min, with melt index ranges from any lower limit toany upper limit being within the scope of the invention.

[0016] As used herein, the terms “metallocene-catalyzed VLDPE,”“metallocene-produced VLDPE,” or “mVLDPE” refer to a VLDPE polymerhaving the density and melt index properties described herein, and beingproduced in the presence of a metallocene catalyst. One skilled in theart will recognize that a metallocene-catalyzed VLDPE polymer hasmeasurable properties distinguishable from a VLDPE polymer having thesame comonomers in the same weight percentages but produced from adifferent process, such as a conventional Ziegler-Natta polymerizationprocess.

[0017] The terms “metallocene” and “metallocene catalyst precursor” asused herein mean compounds having a Group 4, 5 or 6 transition metal(M), with a cyclopentadienyl (Cp) ligand or ligands which may besubstituted, at least one non-cyclopentadienyl-derived ligand (X), andzero or one heteroatom-containing ligand (Y), the ligands beingcoordinated to M and corresponding in number to the valence thereof. Themetallocene catalyst precursors generally require activation with asuitable co-catalyst (referred to as an “activator”), in order to yieldan “active metallocene catalyst”, i.e., an organometallic complex with avacant coordination site that can coordinate, insert, and polymerizeolefins. The metallocene catalyst precursor is preferably one of, or amixture of metallocene compounds of either or both of the followingtypes:

[0018] Cyclopentadienyl (Cp) complexes which have two Cp ring systemsfor ligands. The Cp ligands form a sandwich complex with the metal andcan be free to rotate (unbridged) or locked into a rigid configurationthrough a bridging group. The Cp ring ligands can be like or unlike,unsubstituted, substituted, or a derivative thereof, such as aheterocyclic ring system which may be substituted, and the substitutionscan be fused to form other saturated or unsaturated rings systems suchas tetrahydroindenyl, indenyl, or fluorenyl ring systems. Thesecyclopentadienyl complexes have the general formula

(Cp¹R¹ _(m))R³ _(n)(Cp²R² _(p))MX_(q)

[0019] wherein: Cp¹ and Cp² are the same or different cyclopentadienylrings; R¹ and R² are each, independently, a halogen or a hydrocarbyl,halocarbyl, hydrocarbyl-substituted organometalloid orhalocarbyl-substituted organometalloid group containing up to about 20carbon atoms; m is 0 to 5; p is 0 to 5; two R¹ and/or R² substituents onadjacent carbon atoms of the cyclopentadienyl ring associated therewithcan be joined together to form a ring containing from 4 to about 20carbon atoms; R³ is a bridging group; n is the number of atoms in thedirect chain between the two ligands and is 0 to 8, preferably 0 to 3; Mis a transition metal having a valence of from 3 to 6, preferably fromgroup 4, 5, or 6 of the periodic table of the elements and is preferablyin its highest oxidation state; each X is a non-cyclopentadienyl ligandand is, independently, a hydrogen, a halogen or a hydrocarbyl,oxyhydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid,oxyhydrocarbyl-substituted organometalloid or halocarbyl-substitutedorganometalloid group containing up to about 20 carbon atoms; and q isequal to the valence of M minus 2.

[0020] Monocyclopentadienyl complexes which have only one Cp ring systemas a ligand. The Cp ligand forms a half-sandwich complex with the metaland can be free to rotate (unbridged) or locked into a rigidconfiguration through a bridging group to a heteroatom-containingligand. The Cp ring ligand can be unsubstituted, substituted, or aderivative thereof such as a heterocyclic ring system which may besubstituted, and the substitutions can be fused to form other saturatedor unsaturated rings systems such as tetrahydroindenyl, indenyl, orfluorenyl ring systems. The heteroatom containing ligand is bound toboth the metal and optionally to the Cp ligand through the bridginggroup. The heteroatom itself is an atom with a coordination number ofthree from Group 15 or a coordination number of two from group 16 of theperiodic table of the elements. These mono-cyclopentadienyl complexeshave the general formula

(Cp¹R¹ _(m))R³ _(n)(Y_(r)R²)MX_(s)

[0021] wherein: each R¹ is independently, a halogen or a hydrocarbyl,halocarbyl, hydrocarbyl-substituted organometalloid orhalocarbyl-substituted organometalloid group containing up to about 20carbon atoms, “m” is 0 to 5, and two R¹ substituents on adjacent carbonatoms of the cyclopentadienyl ring associated there with can be joinedtogether to form a ring containing from 4 to about 20 carbon atoms; R³is a bridging group; “n” is 0 to 3; M is a transition metal having avalence of from 3 to 6, preferably from group 4, 5, or 6 of the periodictable of the elements and is preferably in its highest oxidation state;Y is a heteroatom containing group in which the heteroatom is an elementwith a coordination number of three from Group 15 or a coordinationnumber of two from group 16, preferably nitrogen, phosphorous, oxygen,or sulfur; R² is a radical selected from a group consisting of C₁ to C₂₀hydrocarbon radicals, substituted C₁ to C₂₀ hydrocarbon radicals,wherein one or more hydrogen atoms is replaced with a halogen atom, andwhen Y is three coordinate and unbridged there may be two R² groups on Yeach independently a radical selected from the group consisting of C₁ toC₂₀ hydrocarbon radicals, substituted C₁ to C₂₀ hydrocarbon radicals,wherein one or more hydrogen atoms is replaced with a halogen atom, andeach X is a non-cyclopentadienyl ligand and is, independently, ahydrogen, a halogen or a hydrocarbyl, oxyhydrocarbyl, halocarbyl,hydrocarbyl-substituted organo-metalloid, oxyhydrocarbyl-substitutedorganometalloid or halocarbyl-substituted organometalloid groupcontaining up to about 20 carbon atoms, “s” is equal to the valence of Mminus 2.

[0022] Examples of biscyclopentadienyl metallocenes of the typedescribed in group (1) above for producing the mVLDPE polymers of theinvention are disclosed in U.S. Pat. Nos. 5,324,800; 5,198,401;5,278,119; 5,387,568; 5,120,867; 5,017,714; 4,871,705; 4,542,199;4,752,597; 5,132,262; 5,391,629; 5,243,001; 5,278,264; 5,296,434; and5,304,614.

[0023] Illustrative, but not limiting, examples of suitablebiscyclopentadienyl metallocenes of the type described in group (1)above are the racemic isomers of:

[0024] μ-(CH₃)₂Si(indenyl)₂M(Cl)₂;

[0025] μ-(CH₃)₂Si(indenyl)₂M(CH₃)₂;

[0026] μ-(CH₃)₂Si(tetrahydroindenyl)₂M(Cl)₂;

[0027] μ-(CH₃)₂Si(tetrahydroindenyl)₂M(CH₃)₂;

[0028] μ-(CH₃)₂Si(indenyl)₂M(CH₂CH₃)₂; and

[0029] μ-(C₆H₅)₂C(indenyl)₂M(CH₃)₂;

[0030] wherein M is Zr or Hf.

[0031] Examples of suitable unsymmetrical cyclopentadienyl metallocenesof the type described in group (1) above are disclosed in U.S. Pat. Nos.4,892,851; 5,334,677; 5,416,228; and 5,449,651; and in the publicationJ. Am. Chem. Soc. 1988, 110, 6255.

[0032] Illustrative, but not limiting, examples of preferredunsymmetrical cyclopentadienyl metallocenes of the type described ingroup (1) above are:

[0033] μ-(C₆H₅)₂C(cyclopentadienyl)(fluorenyl)M(R)₂;

[0034] μ-(C₆H₅)₂C(3-methylcyclopentadienyl)(fluorenyl)M(R)₂;

[0035] μ-(CH₃)₂C(cyclopentadienyl)(fluorenyl)M(R)₂;

[0036] μ-(C₆H₅)₂C(cyclopentadienyl)(2-methylindenyl)M(CH₃)₂;

[0037] μ-(C₆H₅)₂C(3-methylcyclopentadienyl)(2-methylindenyl)M(Cl)₂;

[0038] μ-(C₆H₅)₂C(cyclopentadienyl)(2,7-dimethylfluorenyl)M(R)₂; and

[0039] μ-(CH₃)₂C(cyclopentadienyl)(2,7-dimethylfluorenyl)M(R)₂;

[0040] wherein M is Zr or Hf, and R is Cl or CH₃.

[0041] Examples of suitable monocyclopentadienyl metallocenes of thetype described in group (2) above are disclosed in U.S. Pat. Nos.5,026,798; 5,057,475; 5,350,723; 5,264,405; 5,055,438; and in WO96/002244.

[0042] Illustrative, but not limiting, examples of preferredmonocyclopentadienyl metallocenes of the type described in group (2)above are:

[0043] μ-(CH₃)₂Si(cyclopentadienyl)(1-adamantylamido)M(R)₂;

[0044] μ-(CH₃)₂Si(3-tertbutylcyclopentadienyl)(1-adamantylamido)M(R)₂;

[0045] μ-(CH₂(tetramethylcyclopentadienyl)(1-adamantylamido)M(R)₂;

[0046] μ-(CH₃)₂Si(tetramethylcyclopentadienyl)(1-adamantylamido)M(R)₂;

[0047] μ-(CH₃)₂C(tetramethylcyclopentadienyl)(1-adamantylamido)M(R)₂;

[0048] μ-(CH₃)₂Si(tetramethylcyclopentadienyl)(1-tertbutylamido)M(R)₂;

[0049] μ-(CH₃)₂Si(fluorenyl)(1-tertbutylamido)M(R)₂;

[0050]μ-(CH₃)₂Si(tetramethylcyclopentadienyl)(1-cyclododecylamido)M(R)₂; and

[0051]μ-(C₆H₅)₂C(tetramethylcyclopentadienyl)(1-cyclododecylamido)M(R)₂;

[0052] wherein M is Ti, Zr or Hf, and R is Cl or CH₃.

[0053] Other organometallic complexes that are useful catalysts for themVLDPE polymers described herein are those with diimido ligand systems,such as are described in WO 96/23010. Other references describingsuitable organometallic complexes include Organometallics, 1999, 2046;PCT publications WO 99/14250, WO 98/50392, WO 98/41529, WO 98/40420, WO98/40374, WO 98/47933; and European publications EP 0 881 233 and EP 0890 581.

[0054] The metallocene compounds and/or other organometallic complexesare contacted with an activator to produce an active catalyst. One classof activators is noncoordinating anions, where the term “noncoordinatinganion” (NCA) means an anion which either does not coordinate to thetransition metal cation or which is only weakly coordinated to thetransition metal cation, thereby remaining sufficiently labile to bedisplaced by a neutral Lewis base. “Compatible” noncoordinating anionsare those which are not degraded to neutrality when the initially formedcomplex decomposes. Further, the anion will not transfer an anionicsubstituent or fragment to the cation so as to cause it to form aneutral four coordinate metallocene compound and a neutral by-productfrom the anion. Noncoordinating anions useful in accordance with thisinvention are those which are compatible, stabilize the metallocenecation in the sense of balancing its ionic charge in a +1 state, yetretain sufficient lability to permit displacement by an ethylenically oracetylenically unsaturated monomer during polymerization. Additionally,the anions useful in this invention will be large or bulky in the senseof sufficient molecular size to largely inhibit or preventneutralization of the metallocene cation by Lewis bases other than thepolymerizable monomers that may be present in the polymerizationprocess. Typically the anion will have a molecular size of greater thanor equal to about 4 angstroms.

[0055] An additional method of making metallocene catalysts usesionizing anionic pre-cursors which are initially neutral Lewis acids butform the cation and anion upon ionizing reaction with the metallocenecompounds. For example, tris(pentafluorophenyl) boron acts to abstractan alkyl, hydride or silyl ligand from the metallocene compound to yielda metallocene cation and a stabilizing non-coordinating anion; see,EP-A-0 427 697 and EP-A-0 520 732. Metallocene catalysts for additionpolymerization can also be prepared by oxidation of the metal centers oftransition metal compounds by anionic precursors containing metallicoxidizing groups along with the anion groups; see EP-A-0 495 375.

[0056] Examples of suitable activators capable of ionic cationization ofthe metallocene compounds of the invention, and consequent stabilizationwith a resulting noncoordinating anion, include:

[0057] trialkyl-substituted ammonium salts such as:

[0058] triethylammonium tetraphenylborate;

[0059] tripropylammonium tetraphenylborate;

[0060] tri(n-butyl)ammonium tetraphenylborate;

[0061] trimethylammonium tetrakis(p-tolyl)borate;

[0062] trimethylammonium tetrakis(o-tolyl)borate;

[0063] tributylammonium tetrakis(pentafluorophenyl)borate;

[0064] tripropylammonium tetrakis(o,p-dimethylphenyl)borate;

[0065] tributylammonium tetrakis(m,m-dimethylphenyl)borate;

[0066] tributylammonium tetrakis(p-trifluoromethylphenyl)borate;

[0067] tributylammonium tetrakis(pentafluorophenyl)borate; and

[0068] tri(n-butyl)ammonium tetrakis(o-tolyl)borate;

[0069] N,N-dialkyl anilinium salts such as:

[0070] N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate;

[0071] N,N-dimethylaniliniumtetrakis(heptafluoronaphthyl)borate;

[0072] N,N-dimethylanilinium tetrakis(perfluoro-4-biphenyl)borate;

[0073] N,N-dimethylanilinium tetraphenylborate;

[0074] N,N-diethylanilinium tetraphenylborate; and

[0075] N,N-2,4,6-pentamethylanilinium tetraphenylborate;

[0076] dialkyl ammonium salts such as:

[0077] di-(isopropyl)ammonium tetrakis(pentafluorophenyl)borate; and

[0078] dicyclohexylammonium tetraphenylborate; and

[0079] triaryl phosphonium salts such as:

[0080] triphenylphosphonium tetraphenylborate;

[0081] tri(methylphenyl)phosphonium tetraphenylborate; and

[0082] tri(dimethylphenyl)phosphonium tetraphenylborate.

[0083] Further examples of suitable anionic precursors include thoseincluding a stable carbonium ion, and a compatible non-coordinatinganion. These include:

[0084] tropillium tetrakis(pentafluorophenyl)borate;

[0085] triphenylmethylium tetrakis(pentafluorophenyl)borate;

[0086] benzene (diazonium) tetrakis(pentafluorophenyl)borate;

[0087] tropillium phenyltris(pentafluorophenyl)borate;

[0088] triphenylmethylium phenyl-(trispentafluorophenyl)borate;

[0089] benzene (diazonium) phenyl-tris(pentafluorophenyl)borate;

[0090] tropillium tetrakis(2,3,5,6-tetrafluorophenyl)borate;

[0091] triphenylmethylium tetrakis(2,3,5,6-tetrafluorophenyl)borate;

[0092] benzene (diazonium) tetrakis(3,4,5-trifluorophenyl)borate;

[0093] tropillium tetrakis(3,4,5-trifluorophenyl)borate;

[0094] benzene (diazonium) tetrakis(3,4,5-trifluorophenyl)borate;

[0095] tropillium tetrakis(3,4,5-trifluorophenyl)aluminate;

[0096] triphenylmethylium tetrakis(3,4,5-trifluorophenyl)aluminate;

[0097] benzene (diazonium) tetrakis(3,4,5-trifluorophenyl)aluminate;

[0098] tropillinum tetrakis(1,2,2-trifluoroethenyl)borate;

[0099] triphenylmethylium tetrakis(1,2,2-trifluoroethenyl)borate;

[0100] benzene (diazonium) tetrakis(1,2,2-trifluoroethenyl)borate;

[0101] tropillium tetrakis(2,3,4,5-tetrafluorophenyl)borate;

[0102] triphenylmethylium tetrakis(2,3,4,5-tetrafluorophenyl)borate; and

[0103] benzene (diazonium) tetrakis(2,3,4,5-tetrafluorophenyl)borate.

[0104] Where the metal ligands include halide moieties, for example,(methyl-phenyl)silylene(tetra-methyl-cyclopentadienyl)(tert-butyl-amido) zirconiumdichloride), which are not capable of ionizing abstraction understandard conditions, they can be converted via known alkylationreactions with organometallic compounds such as lithium or aluminumhydrides or alkyls, alkylalumoxanes, Grignard reagents, etc. See EP-A-0500 944, EP-A1-0 570 982 and EP-A1-0 612 768 for processes describingthe reaction of alkyl aluminum compounds with dihalide substitutedmetallocene compounds prior to or with the addition of activatinganionic compounds. For example, an aluminum alkyl compound may be mixedwith the metallocene prior to its introduction into the reaction vessel.Since the alkyl aluminum is also suitable as a scavenger (as describedbelow), its use in excess of that normally stoichiometrically requiredfor akylation of the metallocene will permit its addition to thereaction solvent with the metallocene compound. Normally, alumoxanewould not be added with the metallocene, so as to avoid prematureactivation, but can be added directly to the reaction vessel in thepresence of the polymerizable monomers when serving as both scavengerand alkylating activator.

[0105] Alkylalumoxanes are additionally suitable as catalyst activators,particularly for those metallocenes having halide ligands. An alumoxaneuseful as a catalyst activator typically is an oligomeric aluminumcompound represented by the general formula (R—Al—O)_(n), which is acyclic compound, or R(R—Al—O)_(n)AlR₂, which is a linear compound. Inthese formulae, each R or R₂ is a C₁ to C₅ alkyl radical, for example,methyl, ethyl, propyl, butyl or pentyl, and “n” is an integer from 1 toabout 50. Most preferably, R is methyl and “n” is at least 4, i.e.,methylalumoxane (MAO). Alumoxanes can be prepared by various proceduresknown in the art. For example, an aluminum alkyl may be treated withwater dissolved in an inert organic solvent, or it may be contacted witha hydrated salt, such as hydrated copper sulfate suspended in an inertorganic solvent, to yield an alumoxane. Generally, however prepared, thereaction of an aluminum alkyl with a limited amount of water yields amixture of the linear and cyclic species of the alumoxane.

[0106] Optionally, a scavenging compound is also used. The term“scavenging compound” as used herein refers to those compounds effectivefor removing polar impurities from the reaction solvent. Such impuritiescan be inadvertently introduced with any of the polymerization reactioncomponents, particularly with solvent, monomer and comonomer feed, andadversely affect catalyst activity and stability by decreasing or eveneliminating catalytic activity, particularly when a metallocenecation-noncoordinating anion pair is the catalyst system. The polarimpurities, or catalyst poisons, include water, oxygen, oxygenatedhydrocarbons, metal impurities, etc. Preferably, steps are taken beforeprovision of such into the reaction vessel, for example, by chemicaltreatment or careful separation techniques after or during the synthesisor preparation of the various components, but some minor amounts ofscavenging compound will still normally be required in thepolymerization process itself. Typically, the scavenging compound willbe an organometallic compound such as the Group-13 organometalliccompounds of U.S. Pat. Nos. 5,153,157 and 5,241,025; EP-A-0 426 638;WO-A-91/09882; WO-A-94/03506; and WO-A-93/14132. Exemplary compoundsinclude triethyl aluminum, triethyl borane, tri-isobutyl aluminum,isobutyl aluminumoxane, those having bulky substituents covalently boundto the metal or metalloid center being preferred to minimize adverseinteraction with the active catalyst.

[0107] The catalyst system is optionally supported, typically on aninorganic oxide or chloride or a material such as polyethylene,polypropylene or polystyrene. These catalysts can include partiallyand/or fully activated precursor compositions. The catalysts may bemodified by prepolymerization or encapsulation. Specific metallocenesand catalyst systems useful in practicing the invention are disclosed inWO 96/11961, and WO 96/11960. Other non-limiting examples of metallocenecatalysts and catalyst systems are discussed in U.S. Pat. Nos.4,808,561, 5,017,714, 5,055,438, 5,064,802, 5,124,418, 5,153,157 and5,324,800. Still other organometallic complexes and/or catalyst systemsare described in Organometallics, 1999, 2046; PCT publications WO96/23010, WO 99/14250, WO 98/50392, WO 98/41529, WO 98/40420, WO98/40374, WO 98/47933; and European publications EP 0 881 233 and EP 0890 581.

[0108] In a preferred embodiment, the mVLDPE polymer is made using agas-phase, metallocene-catalyzed polymerization process. As used herein,the term “gas phase polymerization” refers to polymerization of monomersin a fluidized bed. In this embodiment, the mVLDPE polymer may be madeby polymerizing alpha-olefins in the presence of a metallocene catalystunder reactive conditions in a gas phase reactor having a fluidized bedand a fluidizing medium. In a specific embodiment, the mVLDPE polymercan be made by polymerization in a single reactor (as opposed tomultiple reactors). As discussed in greater detail below, a variety ofgas phase polymerization processes may be used. For example,polymerization may be conducted in uncondensed or “dry” mode, condensedmode, or “super-condensed mode.” In a specific embodiment, the liquid inthe fluidizing medium can be maintained at a level greater than 2 weightpercent based on the total weight of the fluidizing medium.

[0109] The material exiting the reactor includes the mVLDPE polymer anda stream containing unreacted monomer gases. Following polymerization,the polymer is recovered. In certain embodiments, the stream can becompressed and cooled, and mixed with feed components, whereupon a gasphase and a liquid phase are then returned to the reactor.

[0110] Generally, in carrying out the gas phase polymerization processesdescribed herein, the reactor temperature can be in the range of 50° C.to 110° C., sometimes higher. However, the reactor temperature shouldnot exceed the melting point of the mVLDPE being formed. A typicalreactor temperature is 80° C. The reactor pressure should be 100 to 1000psig (0.7 to 7 MPa), preferably 150 to 600 psig (1 to 4 MPa), morepreferably 200 to 500 psig (1.4 to 3.5 MPa) and most preferably 250 to400 psig (1.7 to 2.8 MPa).

[0111] Preferably, the process is operated in a continuous cycle. Aspecific, non-limiting embodiment of the gas phase polymerizationprocess that is operated in a continuous cycle will now be described, itbeing understood that other forms of gas polymerization may also beused.

[0112] A gaseous stream containing one or more monomers is continuouslypassed through a fluidized bed under reactive conditions in the presenceof a catalyst as described above. This gaseous stream is withdrawn fromthe fluidized bed and recycled back into the reactor. Simultaneously,polymer product may be withdrawn from the reactor and new monomer ormonomers are added to replace the reacted monomer(s). In one part of thecycle, in a reactor, a cycling gas stream is heated by the heat ofpolymerization. This heat is removed in another part of the cycle by acooling system external to the reactor. Heat generated by the reactionmay be removed in order to maintain the temperature of the gaseousstream inside the reactor at a temperature below the polymer andcatalyst degradation temperatures. Further, it is often desirable toprevent agglomeration or formation of chunks of polymer that cannot beremoved as product. This may be accomplished in a variety of ways knownin the art, such as, for example, through control of the temperature ofthe gaseous stream in the reaction bed to a temperature below the fusionor sticking temperature of the polymer particles produced during thepolymerization reaction.

[0113] Heat should be removed, since the amount of polymer produced inthe fluidized bed polymerization process is generally related to theamount of heat that can be withdrawn from a reaction zone in a fluidizedbed within the reactor. During the gas phase polymerization process,heat can be removed from the gaseous recycle stream by cooling thestream outside the reactor. The velocity of the gaseous recycle streamin a fluidized bed process should be sufficient to maintain thefluidized bed in a fluidized state. In certain conventional fluidizedbed reactors, the amount of fluid circulated to remove the heat ofpolymerization is often greater than the amount of fluid required forsupport of the fluidized bed and for adequate mixing of the solids inthe fluidized bed. However, to prevent excessive entrainment of solidsin a gaseous stream withdrawn from the fluidized bed, the velocity ofthe gaseous stream should be regulated.

[0114] The recycle stream can be cooled to a temperature below the dewpoint, resulting in condensing a portion of the recycle stream, asdescribed in U.S. Pat. Nos. 4,543,399 and 4,588,790. As set forth inthose patents, the resulting stream containing entrained liquid shouldbe returned to the reactor without the aforementioned agglomerationand/or plugging that may occur when a liquid is introduced during thefluidized bed polymerization process. For purposes of this patent, thisintentional introduction of a liquid into a recycle stream or reactorduring the process is referred to generally as a “condensed mode”operation of the gas phase polymerization process. As taught by theabove mentioned patents, when a recycle stream temperature is lowered toa point below its dew point in condensed mode operation, an increase inpolymer production is possible, as compared to production in a“non-condensing” or “dry” mode, because of increased cooling capacity.Also, a substantial increase in space time yield, the amount of polymerproduction in a given reactor volume, can be achieved by operating incondensed mode with little or no change in product properties. Also, incertain condensed mode operations, the liquid phase of the two-phasegas/liquid recycle stream mixture remains entrained or suspended in thegas phase of the mixture. The cooling of the recycle stream to producethis two-phase mixture results in a liquid/vapor equilibrium.Vaporization of the liquid occurs when heat is added or pressure isreduced. The increase in space time yields are the result of thisincreased cooling capacity of the recycle stream which, in turn, is dueboth to the greater temperature differential between the enteringrecycle stream and the fluidized bed temperature and to the vaporizationof condensed liquid entrained in the recycle stream. In a specificnon-limiting embodiment of the process described herein, a condensedmode of operation is utilized.

[0115] In operating the gas phase polymerization process to obtain themVLDPE polymer, the amount of polymer and catalyst, the operatingtemperature of the reactor, the ratio of comonomer(s) to monomer and theratio of hydrogen to monomer should be determined in advance, so thatthe desired density and melt index can be achieved.

[0116] Although a variety of gas polymerization processes may be used tomake the polyolefins of the present inventions, including non-condensedor dry mode, it is preferred to use any one of a variety of condensedmode processes, including the condensed mode processes described in theabove patents, as well as improved condensed mode gas polymerizationprocesses, such as those disclosed in U.S. Pat. Nos. 5,462,999, and5,405,922. Other types of condensed mode processes are also applicable,including so-called “supercondensed mode” processes, as discussed inU.S. Pat. Nos. 5,352,749 and 5,436,304.

[0117] The condensable fluids that can be used in one of the condensedmode gas phase polymerization operations may include saturated orunsaturated hydrocarbons. Examples of suitable inert condensable fluidsare readily volatile liquid hydrocarbons, which may be selected fromsaturated hydrocarbons containing from 2 to 8 carbon atoms. Somesuitable saturated hydrocarbons are propane, n-butane, isobutane,n-pentane, isopentane, neopentane, n-hexane, isohexane, and othersaturated C₆ hydrocarbons, n-heptane, n-octane and other saturated C₇and C₈ hydrocarbons, or mixtures thereof. The preferred inertcondensable hydrocarbons are C₄ and C₆ saturated hydrocarbons. Thecondensable fluids may also include polymerizable condensable comonomerssuch as olefins, alpha-olefins, diolefins, diolefins containing at leastone alpha-olefin or mixtures thereof including some of theaforementioned monomers which may be partially or entirely incorporatedinto the polymer product.

[0118] The preferred gas-phase, metallocene VLDPE polymers can befurther characterized by a narrow composition distribution. As is wellknown to those skilled in the art, the composition distribution of acopolymer relates to the uniformity of distribution of comonomer amongthe molecules of the polymer. Metallocene catalysts are known toincorporate comonomer very evenly among the polymer molecules theyproduce. Thus, copolymers produced from a catalyst system having asingle metallocene component have a very narrow compositiondistribution, in that most of the polymer molecules will have roughlythe same comonomer content, and within each molecule the comonomer willbe randomly distributed. By contrast, conventional Ziegler-Nattacatalysts generally yield copolymers having a considerably broadercomposition distribution, with comonomer inclusion varying widely amongthe polymer molecules.

[0119] A measure of composition distribution is the “CompositionDistribution Breadth Index” (“CDBI”). The definition of CompositionDistribution Breadth Index (CDBI), and the method of determining CDBI,can be found in U.S. Pat. No. 5,206,075 and PCT publication WO 93/03093.From the weight fraction versus composition distribution curve, the CDBIis determined by establishing the weight percentage of a sample that hasa comonomer content within 50% of the median comonomer content on eachside of the median. The CDBI of a copolymer is readily determinedutilizing well known techniques for isolating individual fractions of asample of the copolymer. One such technique is Temperature RisingElution Fractionation (TREF) as described in Wild, et al., J. Poly.Sci., Poly. Phys. Ed., vol. 20, p. 441 (1982).

[0120] To determine CDBI, a solubility distribution curve is firstgenerated for the copolymer. This may be accomplished using dataacquired from the TREF technique described above. This solubilitydistribution curve is a plot of the weight fraction of the copolymerthat is solubilized as a function of temperature. This is converted to aweight fraction versus composition distribution curve. For the purposeof simplifying the correlation of composition with elution temperature,all fractions are assumed to have a Mn≧15,000, where Mn is the numberaverage molecular weight of the fraction. Any low weight fractionspresent generally represent a trivial portion of the mVLDPE polymers.The remainder of this description and the appended claims maintain thisconvention of assuming all fractions have Mn≧15,000 in the CDBImeasurement.

[0121] The mVLDPE polymers can also be characterized by molecular weightdistribution (MWD). Molecular weight distribution (MWD) is a measure ofthe range of molecular weights within a given polymer sample. It is wellknown that the breadth of the MWD can be characterized by the ratios ofvarious molecular weight averages, such as the ratio of the weightaverage molecular weight to the number average molecular weight, Mw/Mn,or the ratio of the Z-average molecular weight to the weight averagemolecular weight, Mz/Mw.

[0122] Mz, Mw and Mn can be measured using gel permeation chromatography(GPC), also known as size exclusion chromatography (SEC). This techniqueutilizes an instrument containing columns packed with porous beads, anelution solvent, and detector in order to separate polymer molecules ofdifferent sizes. In a typical measurement, the GPC instrument used is aWaters chromatograph equipped with ultrastyro gel columns operated at145° C. The elution solvent used is trichlorobenzene. The columns arecalibrated using sixteen polystyrene standards of precisely knownmolecular weights. A correlation of polystyrene retention volumeobtained from the standards, to the retention volume of the polymertested yields the polymer molecular weight.

[0123] Average molecular weights M can be computed from the expression:$M = \frac{\sum\limits_{i}{N_{i}M_{i}^{n + 1}}}{\sum\limits_{i}{N_{i}M_{i}^{n}}}$

[0124] where N_(i) is the number of molecules having a molecular weightM_(i). When n=0, M is the number average molecular weight Mn. When n=1,M is the weight average molecular weight Mw. When n=2, M is theZ-average molecular weight Mz. The desired MWD function (e.g., Mw/Mn orMz/Mw) is the ratio of the corresponding M values. Measurement of M andMWD is well known in the art and is discussed in more detail in, forexample, Slade, P. E. Ed., Polymer Molecular Weights Part II, MarcelDekker, Inc., NY, (1975) 287-368; Rodriguez, F., Principles of PolymerSystems 3rd ed., Hemisphere Pub. Corp., NY, (1989) 155-160; U.S. Pat.No. 4,540,753; Verstrate et al., Macromolecules, vol. 21, (1988) 3360;and references cited therein.

[0125] The mVLDPE polymers are preferably linear polymers without longchain branching. As used in the present disclosure, the term “linear” isapplied to a polymer that has a linear backbone and does not have longchain branching; i.e., a “linear” polymer is one that does not have thelong chain branches characteristic of a SLEP polymer as defined in U.S.Pat. Nos. 5,272,236 and 5,278,272. Thus, a “substantially linear”polymer as disclosed in those patents is not a “linear” polymer becauseof the presence of long chain branching.

[0126] In one embodiment, the mVLDPE polymer has one or more of thefollowing characteristics, in addition to the density and otherparameters described herein:

[0127] a composition distribution CDBI in a range from a lower limit of50% or 55% or 60% to an upper limit of 85%, or 80%, or 75%, or 70%, withranges from any lower limit to any upper limit being contemplated;

[0128] a molecular weight distribution Mw/Mn of 2 to 3, alternatively2.2 to 2.8;

[0129] a molecular weight distribution Mz/Mw of less than 2; and

[0130] the presence of two peaks in a TREF measurement.

[0131] Particularly preferred mVLDPEs having some or all of thesecharacteristics are the gas phase metallocene-produced VLDPEs describedabove.

[0132] Two peaks in the TREF measurement as used in this specificationand the appended claims means the presence of two distinct normalizedELS (evaporation mass light scattering) response peaks in a graph ofnormalized ELS response (vertical or y axis) versus elution temperature(horizontal or x axis with temperature increasing from left to right)using the TREF method disclosed in the EXAMPLES section below. A “peak”in this context means where the general slope of the graph changes frompositive to negative with increasing temperature. Between the two peaksis a local minimum in which the general slope of the graph changes fromnegative to positive with increasing temperature. “General trend” of thegraph is intended to exclude the multiple local minimums and maximumsthat can occur in intervals of 2° C. or less. Preferably, the twodistinct peaks are at least 3° C. apart, more preferably at least 4° C.apart, even more preferably at least 5° C. apart. Additionally, both ofthe distinct peaks occur at a temperature on the graph above 20° C. andbelow 120° C. where the elution temperature is run to 0° C. or lower.This limitation avoids confusion with the apparent peak on the graph atlow temperature caused by material that remains soluble at the lowestelution temperature. Two peaks on such a graph indicates a bi-modalcomposition distribution (CD). Bimodal CD may also be determined byother methods known to those skilled in the art. One such alternatemethod for TREF measurement than can be used if the above method doesnot show two peaks is disclosed in B. Monrabal, “CrystallizationAnalysis Fractionation: A New Technique for the Analysis of BranchingDistribution in Polyolefins,” Journal of Applied Polymer Science, Vol.52, 491-499 (1994).

[0133] A preferred balance of properties, particularly in filmapplications, according to the invention is achieved when the long chainbranching of the mVLDPE is reduced. Therefore, with respect to thecatalyst structures described above, bis-Cp structures are preferredover mono-Cp structures, unbridged structures are preferred over bridgedstructures, and unbridged bis-Cp structures are the most preferred.Preferred catalyst systems which will minimize or eliminate long chainbranching to produce polymers substantially free of or free of longchain branching are based on un-bridged bis-Cp zirconocenes, such as butnot limited to bis (1-methyl-3-n-butyl cyclopentadiane) zirconiumdichloride.

[0134] Symmetric metallocenes may be used to produce an mVLDPE polymerof the present invention. Symmetric metallocenes include, but are notlimited to:

[0135] bis(methylcyclopentadienyl)zirconium dichloride,

[0136] bis(1,3-dimethylcyclopentadienyl)zirconium dichloride,

[0137] bis(1,2-dimethylcyclopentadienyl)zirconium dichloride,

[0138] bis(1,2,4-trimethylcyclopentadienyl)zirconium dichloride,

[0139] bis(1,2,3-trimethylcyclopentadienyl)zirconium dichloride,

[0140] bis(tetramethylcyclopentadienyl)zirconium dichloride,

[0141] bis(pentamethylcyclopentadienyl)zirconium dichloride,

[0142] bis(ethylcyclopentadienyl)zirconium dichloride,

[0143] bis(propylcyclopentadienyl)zirconium dichloride,

[0144] bis(butylcyclopentadienyl)zirconium dichloride,

[0145] bis(isobutylcyclopentadienyl)zirconium dichloride,

[0146] bis(pentylcyclopentadienyl)zirconium dichloride,

[0147] bis(isopentylcyclopentadienyl)zirconium dichloride,

[0148] bis(cyclopentylcyclopentadienyl)zirconium dichloride

[0149] bis(phenylcyclopentadienyl)zirconium dichloride,

[0150] bis(benzylcyclopentadienyl)zirconium dichloride,

[0151] bis(trimethylsilylmethylcyclopentadienyl)zirconium dichloride,

[0152] bis(cyclopropylmethylcyclopentadienyl)zirconium dichloride,

[0153] bis(cyclopentylmethylcyclopentadienyl)zirconium dichloride,

[0154] bis(cyclohexylmethylcyclopentadienyl)zirconium dichloride,

[0155] bis(propenylcyclopentadienyl)zirconium dichloride,

[0156] bis(butenylcyclopentadienyl)zirconium dichloride,

[0157] bis(1,3-ethylmethylcyclopentadienyl)zirconium dichloride,

[0158] bis(1,3-propylmethylcyclopentadienyl)zirconium dichloride,

[0159] bis(1,3-butylmethylcyclopentadienyl)zirconium dichloride,

[0160] bis(1,3-isopropylmethylcyclopentadienyl)zirconium dichloride,

[0161] bis(1,3-isobutylmethylcyclopentadienyl)zirconium dichloride,

[0162] bis(1,3-methylcyclopentylcyclopentadienyl)zirconium dichloride,and

[0163] bis(1,2,4-dimethylpropylcyclopentadienyl)zirconium dichloride.

[0164] Unsymmetric metallocenes may be used to produce an mVLDPE polymerof the present invention. Unsymmetric metallocenes include, but are notlimited to:

[0165] cyclopentadienyl(1,3-dimethylcyclopentadienyl)zirconiumdichloride,

[0166] cyclopentadienyl(1,2,4-trimethylcyclopentadienyl)zirconiumdichloride,

[0167] cyclopentadienyl(tetramethylcyclopentadienyl)zirconiumdichloride,

[0168] cyclopentadienyl(pentamethylcyclopentadienyl)zirconiumdichloride,

[0169] cyclopentadienyl(propylcyclopentadienyl)zirconium dichloride,

[0170] cyclopentadienyl(butylcyclopentadienyl)zirconium dichloride,

[0171] cyclopentadienyl(pentylcyclopentadienyl)zirconium dichloride,

[0172] cyclopentadienyl(isobutylcyclopentadienyl)zirconium dichloride,

[0173] cyclopentadienyl(cyclopentylcyclopentadienyl)zirconiumdichloride,

[0174] cyclopentadienyl(isopentylcyclopentadienyl)zirconium dichloride,

[0175] cyclopentadienyl(benzylcyclopentadienyl)zirconium dichloride,

[0176] cyclopentadienyl(phenylcyclopentadienyl)zirconium dichloride,

[0177] cyclopentadienyl(1,3-propylmethylcyclopentadienyl)zirconiumdichloride,

[0178] cyclopentadienyl(1,3-butylmethylcyclopentadienyl)zirconiumdichloride,

[0179] cyclopentadienyl(1,3-isobutylmethylcyclopentadienyl)zirconiumdichloride,

[0180] cyclopentadienyl(1,2,4-dimethylpropylcyclopentadienyl)zirconiumdichloride,

[0181] (tetramethylcyclopentadienyl)(methylcyclopentadienyl)zirconiumdichloride,

[0182](tetramethylcyclopentadienyl)(1,3-dimethylcyclopentadienyl)zirconiumdichloride,

[0183](tetramethylcyclopentadienyl)(1,2,4-trimethylcyclopentadienyl)zirconiumdichloride,

[0184] (tetramethylcyclopentadienyl)(propylcyclopentadienyl)zirconiumdichloride,

[0185](tetramethylcyclopentadienyl)(cyclopentylcyclopentadienyl)zirconiumdichloride,

[0186] (pentamethylcyclopentadienyl)(methylcyclopentadienyl)zirconiumdichloride,

[0187](pentamethylcyclopentadienyl)(1,3-dimethylcyclopentadienyl)zirconiumdichloride,

[0188](pentamethylcyclopentadienyl)(1,2,4-trimethylcyclopentadienyl)zirconiumdichloride,

[0189] (pentamethylcyclopentadienyl)(propylcyclopentadienyl)zirconiumdichloride,

[0190](pentamethylcyclopentadienyl)(cyclopentylcyclopentadienyl)zirconiumdichloride,

[0191] cyclopentadienyl(ethyltetramentylcyclopentadienyl)zirconiumdichloride,

[0192] cyclopentadienyl(propyltetramentylcyclopentadienyl)zirconiumdichloride,

[0193](methylcyclopentadienyl)(propyltetramentylcyclopentadienyl)zirconiumdichloride,

[0194](1,3-dimethylcyclopentadienyl)(propyltetramentylcyclopentadienyl)-zirconiumdichloride,

[0195](1,2,4-trimethylcyclopentadienyl)(propyltetramentylcyclopentadienyl)-zirconiumdichloride,

[0196](propylcyclopentadienyl)(propyltetramentylcyclopentadienyl)zirconiumdichloride,

[0197] cyclopentadienyl(indenyl)zirconium dichloride,

[0198] (methylcyclopentadienyl)(indenyl)zirconium dichloride,

[0199] (1,3-dimethylcyclopentadienyl)(indenyl)zirconium dichloride,

[0200] (1,2,4-trimethylcyclopentadienyl)(indenyl)zirconium dichloride,

[0201] (tetramethylcyclopentadienyl)(indenyl)zirconium dichloride,

[0202] (pentamethylcyclopentadienyl)(indenyl)zirconium dichloride,

[0203] cyclopentadienyl(1-methylindenyl)zirconium dichloride,

[0204] cyclopentadienyl(1,3-dimethylindenyl)zirconium dichloride,

[0205] cyclopentadienyl(1,2,3-trimethylindenyl)zirconium dichloride,

[0206] cyclopentadienyl(4,7-dimethylindenyl)zirconium dichloride,

[0207] (tetramethylcyclopentadienyl)(4,7-dimethylindenyl)zirconiumdichloride,

[0208] (pentamethylcyclopentadienyl)(4,7-dimethylindenyl)zirconiumdichloride,

[0209] cyclopentadienyl(5,6-dimethylindenyl)zirconium dichloride,

[0210] (pentamethylcyclopentadienyl)(5,6-dimethylindenyl)zirconiumdichloride, and

[0211] (tetramethylcyclopentadienyl)(5,6-dimethylindenyl)zirconiumdichloride.

[0212] The preferred method for producing the catalyst is describedbelow and can be found in U.S. application Ser. No. 265,533, filed Jun.24, 1994, now abandoned, and Ser. No. 265,532, filed Jun. 24, 1994, nowabandoned, both of which are hereby incorporated by reference in theirentirety. In a preferred embodiment, the metallocene catalyst componentis typically slurried in a liquid to form a metallocene solution and aseparate solution is formed containing an activator and a liquid. Theliquid can be any compatible solvent or other liquid capable of forminga solution or the like with at least one metallocene catalyst componentand/or at least one activator. In the preferred embodiment the liquid isa cyclic aliphatic or aromatic hydrocarbon, most preferably toluene. Themetallocene and activator solutions are preferably mixed together andadded to a porous support such that the total volume of the metallocenesolution and the activator solution or the metallocene and activatorsolution is less than four times the pore volume of the porous support,more preferably less than three times, even more preferably less thantwo times, and more preferably in the 1-1.5 times to 2.5-4 times rangeand most preferably in the 1.5 to 3 times range. Also, in the preferredembodiment, an antistatic agent is added to the catalyst preparation.

[0213] In one embodiment, the metallocene catalyst is prepared fromsilica dehydrated at 600° C. The catalyst is a commercial scale catalystprepared in a mixing vessel with and agitator. An initial charge of 1156pounds (462 kg) toluene is added to the mixer. This was followed bymixing 925 pounds (421 kg) of 30 percent by weight methyl aluminoxane intoluene. This is followed with 100 pounds (46 kg) of 20 percent byweight bis(1,3-methyl-n-butyl cyclopentadienyl) zirconium dichloride intoluene (20.4 pounds (9.3 kg) of contained metallocene). An additional144 pounds (66 kg) of toluene is added to the mixer to rinse themetallocene feed cylinder and allowed to mix for 30 minutes at ambientconditions. This is followed by 54.3 pounds (25 kg) of an AS-990 intoluene, surface modifier solution, containing 5.3 pounds (2.4 kg) ofcontained AS-990. An additional 100 pounds (46 kg) of toluene rinsed thesurface modifier container and was added to the mixer. The resultingslurry is vacuum dried at 3.2 psia (70.6 kPa) at 175° F. (79° C.) to afree flowing powder. The final catalyst weight was 1093 pounds (497 kg).The catalyst can have a final zirconium loading of 0.40% and an aluminumloading of 12.0%.

[0214] In one preferred embodiment a substantially homogenous catalystsystem is preferred. For the purposes of this patent specification andappended claims, a “substantially homogenous catalyst” is one in whichthe mole ratio of the transition metal of the catalyst component,preferably with an activator, is evenly distributed throughout a poroussupport.

[0215] The procedure for measuring the total pore volume of a poroussupport is well known in the art. Details of one of these procedures isdiscussed in Volume 1, Experimental Methods in Catalytic Research(Academic Press, 1968) (specifically see pages 67-96). This preferredprocedure involves the use of a classical BET apparatus for nitrogenabsorption. Another method well know in the art is described in Innes,Total porosity and Particle Density of Fluid Catalysts By LiquidTitration, Vol. 28, No. 3, Analytical Chemistry 332-334 (March, 1956).

[0216] The mole ratio of the metal of the activator component to thetransition metal of the metallocene component is in the range of ratiosbetween 0.3:1 to 1000:1, preferably 20:1 to 800:1, and most preferably50:1 to 500:1. Where the activator is an ionizing activator aspreviously described the mole ratio of the metal of the activatorcomponent to the transition metal component is preferably in the rangeof ratios between 0.3:1 to 3:1. component to the transition metalcomponent is preferably in the range of ratios between 0.3:1 to 3:1.

[0217] Typically in a gas phase polymerization process a continuouscycle is employed where in one part of the cycle of a reactor, a cyclinggas stream, otherwise known as a recycle stream or fluidizing medium, isheated in the reactor by the heat of polymerization. This heat isremoved in another part of the cycle by a cooling system external to thereactor. (See, for example, U.S. Pat. Nos. 4,543,399, 4,588,790,5,028,670, 5,352,749, 5,405,922, 5,436,304, 5,453,471 and 5,462,999, allof which are fully incorporated herein by reference.)

[0218] Generally in a gas fluidized bed process for producing polymerfrom monomers a gaseous stream containing one or more monomers iscontinuously cycled through a fluidized bed in the presence of acatalyst under reactive conditions. The gaseous stream is withdrawn fromthe fluidized bed and recycled back into the reactor. Simultaneously,polymer product is withdrawn from the reactor and new or fresh monomeris added to replace the polymerized monomer.

[0219] In one embodiment, the mVLDPE is produced by a processessentially free of a scavenger. As used herein, the term “essentiallyfree” means that during the process of the invention no more than 10 ppmof a scavenger based on the total weight of the recycle stream ispresent at any given point in time during the process of the invention.

[0220] In another embodiment, the mVLDPE is produced by a processessentially free of a scavenger. As used herein, the term “essentiallyfree” means that during the process of the invention no more than 50 ppmof a scavenger based on the total weight of the recycle stream ispresent at any given point in time during the process of the invention.

[0221] In one embodiment during reactor start-up to remove impuritiesand ensure polymerization is initiated, a scavenger is present in anamount less than 300 ppm, preferably less than 250 ppm, more preferablyless than 200 ppm, even more preferably less than 150 ppm, still morepreferably less than 100 ppm, and most preferably less than 50 ppm basedon the total bed weight of a fluidized bed during the first 12 hoursfrom the time the catalyst is placed into the reactor, preferably up to6 hours, more preferably less than 3 hours, even more preferably lessthan 2 hours, and most preferably less than 1 hour and then theintroduction of the scavenger is halted.

[0222] In another embodiment, the scavenger is present in an amountsufficient until the catalyst of the invention has achieved a catalystproductivity on a weight ratio basis of greater than 1000 grams ofpolymer per gram of the catalyst, preferably greater than about 1500,more preferably greater than 2000, even more preferably greater than2500, and most preferably greater than 3000.

[0223] In another embodiment, during start-up the scavenger is presentin an amount sufficient until the catalyst of the invention has achieveda catalyst productivity 40 percent of that of steady-state, preferablyless than 30 percent, even more preferably less than 20 percent and mostpreferably less than 10 percent. For the purposes of this patentspecification and appended claims “steady state” is the production rate,weight of polymer being produced per hour.

[0224] The productivity of the catalyst or catalyst system is influencedby the main monomer, (i.e., ethylene or propylene) partial pressure. Thepreferred mole percent of the monomer, ethylene or propylene, is fromabout 25 to 90 mole percent and the monomer partial pressure is in therange of from about 75 psia (520 kPa) to about 300 psia (2100 kPa),which are typical conditions in a gas phase polymerization process.

[0225] When a scavenger is utilized, the scavenger can be introducedtypically into the reactor directly or indirectly into the recyclestream or into any external means capable of introducing the scavengerinto the reactor. Preferably the scavenger enters into the reactordirectly, and most preferably directly into the reactor bed or below thedistributor plate in a typical gas phase process, preferably after thebed is in a fluidized state. In one embodiment the scavenger can beintroduced once, intermittently or continuously to the reactor system.

[0226] The scavenger is introduced to the reactor at a rate equivalentto 10 ppm to 100 ppm based on the steady state, production rate, andthen scavenger introduction is stopped.

[0227] In yet another embodiment particularly during start-up thescavenger when used is introduced at a rate sufficient to provide anincrease in catalyst productivity on a weight ratio basis of a rate of200 grams of polymer per gram of catalyst per minute, preferably at arate of 300, even more preferably at a rate of 400 and most preferablyat a rate of 500.

[0228] In another embodiment, the mole ratio of the metal of thescavenger to the transition metal of the metallocene catalyst componentequals about, about 0.2 multiplied by the ppm of a scavenger based onthe production rate multiplied by the catalyst productivity in kilogramsof polymer per gram of catalyst. The range of the mole ratio is fromabout 300 to 10. In a preferred embodiment, where an alkyl aluminum isused as the scavenger the mole ratio is represented as aluminum (Al) totransition metal, for example, zirconium, where the moles of Al arebased on the total amount of scavenger used.

[0229] It is also preferred that hydrogen not be added to the systemsimultaneously with the scavenger. It is also within the scope of thisinvention that the scavenger can be introduced on a carrier separatefrom that used when a supported metallocene catalyst system is used inthe process of the invention.

[0230] Fines for the purpose of this patent specification and appendedclaims are polymer particles less than 125 μm in size. Fines of thissize can be measured by using a standard 120 mesh unit sieve screen. Ina preferred embodiment the amount of scavenger present in the reactor atany given point in time during the process of the invention the level offines less than 125 μm is less than 10%, preferably less than 1%, morepreferably less than 0.85% to less than 0.05%.

[0231] It is within the scope of the invention that a system external tothe reactor for removing scavengers introduced in the process of theinvention from the recycle stream may be used. This would then preventthe recycle of the scavenger back into the reactor and prevent scavengerbuild-up in the reactor system. It is preferred that such a system isplaced prior to the heat exchanger or compressor in the recycle streamline. It is contemplated that such a system would condense the scavengerout of the fluidizing medium in the recycle stream line. It would bepreferred that the fluidizing medium is treated to remove the scavenger,see for example U.S. Pat. No. 4,460,755, incorporated herein byreference.

[0232] It is also contemplated that scavenger can be intermittentlyintroduced during the process wherein greater than 90%, preferablygreater than 95% of all the scavenger introduced is removed from therecycle stream.

[0233] It is also contemplated that the catalyst or catalyst system orcomponents thereof can be used upon start-up as a scavenger, however,this would be an expensive procedure.

[0234] In the most preferred embodiment, the process is a gas phasepolymerization process operating in a condensed mode. For the purposesof this patent specification and appended claims the process ofpurposefully introducing a recycle stream having a liquid and a gasphase into a reactor such that the weight percent of liquid based on thetotal weight of the recycle stream is greater than about 2.0 weightpercent is defined to be operating a gas phase polymerization process ina “condensed mode”.

[0235] In one embodiment, the weight percent of liquid in the recyclestream based on the total weight of the recycle stream is in the rangeof about 2 to about 50 weight percent, preferably greater than 10 weightpercent and more preferably greater than 15 weight percent and even morepreferably greater than 20 weight percent and most preferably in therange between about 20 and about 40 percent. However, any level ofcondensed can be used depending on the desired production rate.

[0236] In another embodiment, the amount of scavenger utilized if any isused should be in a mole ratio less than 100, preferably less than 50,more preferably less than about 25 based on the mole ratio of the metalof the transition metal scavenger to the transition metal of themetallocene where the scavenger is an aluminum containing organometalliccompound and the transition metal of the metallocene is a Group 4 metalthen the mole ratio above is based on the moles of aluminum to the molesof the Group 4 metal of the catalyst.

[0237] Fouling is a term used to describe the collection of polymerdeposits on surfaces in a reactor. Fouling is detrimental to all partsof a polymerization process, including the reactor and its associatedsystems, hardware, etc. Fouling is especially disruptive in areasrestricting gas flow or liquid flow. The two major areas of primaryconcern are the heat exchanger and distributor plate fouling. The heatexchanger consists of a series of small diameter tubes arranged in atube bundle. The distributor plate is a solid plate containing numeroussmall diameter orifices through which the gas contained in a recyclestream is passed through before entering the reaction zone ordistributed into a bed of solid polymer in a fluidized bed reactor suchas described in U.S. Pat. No. 4,933,149, incorporated herein byreference.

[0238] Fouling manifests itself as an increase in the pressure dropacross either the plate, cooler, or both. Once the pressure drop becomestoo high, gas or liquid can no longer be circulated efficiently by thecompressor, and it is often necessary to shut the reactor down. Cleaningout the reactor can take several days and is very time consuming andcostly. Fouling can also occur in the recycle gas piping and compressor,but usually accompanies plate and cooler fouling.

[0239] To quantify the rate of fouling it is useful to define a foulingfactor, F. F is the fraction of the area of a hole that is fouled. IfF=0 (0%) then there is no fouling. Conversely, if F=1 (100%) the hole iscompletely plugged. It is possible to relate the fouling to the pressuredrop, ΔP, at a given time in terms of the pressure drop of a cleansystem, ΔP₀. As fouling increases, ΔP increases and is larger than theinitial pressure drop, ΔP₀. F is given by the following expressions:$\begin{matrix}{{{Plate}\quad {Fouling}\text{:}\quad F} = {1 - \sqrt{\frac{\Delta \quad P_{0}}{\Delta \quad P}}}} & (I) \\{{{Cooler}\quad {Fouling}\text{:}\quad F} = {1 - \left( \frac{\Delta \quad P_{0}}{\Delta \quad P} \right)^{2/5}}} & ({II})\end{matrix}$

[0240] In general, when F is greater than about 0.3 to about 0.4(30-40%) a reactor shutdown is inevitable. Preferably, F is less than40%, preferably less than 30%, even more preferably less than 20%, stillmore preferably less than 15% and most preferably less than 10% to 0%.The rate of fouling, the change in F as a function of time, is used toquantify fouling. If no fouling occurs the rate of fouling is zero. Aminimum acceptable rate of fouling for a commercial operation is about12 percent/month or 0.4 percent/day, preferably less than 0.3percent/day, even more preferably less than 0.2 percent/day and mostpreferably less than 0.1 percent/day.

[0241] Particle size is determined by determining the weight of thematerial collected on a series of U.S. Standard sieves and determiningthe weight average particle size.

[0242] Fines are defined as the percentage of the total distributionpassing through 120 mesh standard sieve.

[0243] In one embodiment, the process is operated using a metallocenecatalyst based on bis(1,3-methyl-n-butyl cyclopentadienyl) zirconiumdichloride.

[0244] Possible optimizations of the gas phase polymerization processand additional catalyst preparations are disclosed in U.S. Pat. Nos.5,763,543, 6,087,291, and 5,712,352, and PCT published applications WO00/02930 and WO 00/02931.

[0245] Although the VLPDE polymer component of the mVLDPE/polypropyleneblends of the invention has been discussed as a single polymer, blendsof two or more VLDPE polymers, preferably two or more mVLDPE polymers,having the properties described herein are also contemplated.

[0246] The Polypropylene Component

[0247] The polymer blend also includes a polypropylene component (“PP”).The polypropylene component can include one or more polypropylenehomopolymer or copolymer or mixture, of any tacticity. Suitablepolypropylene copolymers include those copolymers commonly termed randomcopolymers (RCP) and impact copolymers (ICP). As used herein unlessindicated otherwise, the term “polypropylene” includes homopolymers andcopolymers.

[0248] The term “polypropylene component” also includes polyolefinmulti-step reactor products wherein an amorphous ethylene propylenerandom copolymer is molecularly dispersed in a predominantlysemi-crystalline high propylene monomer/low ethylene monomer continuousmatrix. Examples of such polymers are described in U.S. Pat. Nos.5,300,365, 5,212,246 and 5,331,047. These materials, referred to hereinas “high rubber content polypropylenes,” are commonly known as Catalloy™resins, and are commercially available from Basell.

[0249] Suitable comonomers include ethylene and α-olefins, such asC₄-C₂₀ α-olefins and preferably ethylene or C₄-C₁₂ α-olefins. Theα-olefin comonomer can be linear or branched, and two or more comonomerscan be used, if desired. Thus, the term “copolymer” as used hereinincludes polymers with more than two types of monomers, such asterpolymers. Examples of suitable comonomers include ethylene, linearC₄-C₂ α-olefins, and α-olefins having one or more C₁-C₃ alkyl branches.Specific examples include ethylene; 3-methyl-1-butene;3,3-dimethyl-1-butene; 1-pentene; 1-pentene with one or more methyl,ethyl or propyl substituents; 1-hexene with one or more methyl, ethyl orpropyl substituents; 1-heptene with one or more methyl, ethyl or propylsubstituents; 1-octene with one or more methyl, ethyl or propylsubstituents; 1-nonene with one or more methyl, ethyl or propylsubstituents; ethyl, methyl or dimethyl-substituted 1-decene, or1-dodecene. Preferred comonomers include ethylene, 1-butene, 1-pentene,3-methyl-1-butene, 1-hexene, 3-methyl-1-pentene, 4-methyl-1-pentene,3,3-dimethyl-1-butene, 1-heptene, 1-hexene with a methyl substituent onany of C₃-C₅, 1-pentene with two methyl substituents in anystoichiometrically acceptable combination on C₃ or C₄,3-ethyl-1-pentene, 1-octene, 1-pentene with a methyl substituent on anyof C₃ or C₄, 1-hexene with two methyl substituents in anystoichiometrically acceptable combination on C₃-C₅, 1-pentene with threemethyl substituents in any stoichiometrically acceptable combination onC₃ or C₄, 1-hexene with an ethyl substituent on C₃ or C₄, 1-pentene withan ethyl substituent on C₃ and a methyl substituent in astoichiometrically acceptable position on C₃ or C₄, 1-decene, 1-nonene,1-nonene with a methyl substituent on any of C₃-C₉, 1-octene with twomethyl substituents in any stoichiometrically acceptable combination onC₃-C₇, 1-heptene with three methyl substituents in anystoichiometrically acceptable combination on C₃-C₆, 1-octene with anethyl substituent on any of C₃-C₇, 1-hexene with two ethyl substituentsin any stoichiometrically acceptable combination on C₃ or C₄, and1-dodecene. It should be appreciated that the list of comonomers aboveis merely exemplary, and is not intended to be limiting. It should alsobe appreciated that terpolymers of propylene can be formed bypolymerizing propylene with the above listed comonomers. A particularlypreferred comonomer is ethylene.

[0250] The weight percentage of comonomer in the polypropylene variesaccording to the type of polypropylene. A polypropylene homopolymer hasno comonomer. A random copolymer can have from a lower limit of 0.5 wt.% or 1 wt. % comonomer to an upper limit of 10 wt. % or 5 wt. % or 4 wt.% or 3 wt. % or 2 wt. % comonomer, with ranges from any lower limit toany upper limit. An impact copolymer can have an overall comonomercontent of from a lower limit of 1 wt. % or 3 wt. % or 4 wt. % or 5 wt.% to an upper limit of 15 wt. % or 12 wt. % or 10 wt. % comonomer, withranges from any lower limit to any upper limit, and a content ofcomonomer in the rubber phase (based on the total weight of the rubberphase) of from a lower limit of 30 wt. % or 40 wt. % or 45 wt. % to anupper limit of 70 wt. % or 60 wt. % or 55 wt. %, with ranges from anylower limit to any upper. A high rubber content polypropylene can have acomonomer content of from a lower limit of 12 wt. % or 15 wt. % or 20wt. % or 30 wt. % to an upper limit of 40 wt. % or 30 wt. % or 20 wt. %,with ranges from any lower limit to any greater upper limit. Thepreferred comonomer is ethylene.

[0251] In some embodiments, the polypropylene component is predominantlycrystalline, and has a melting point greater than 110° C. or greaterthan 115° C. or greater than 130° C.

[0252] In some embodiments, the polypropylene component is predominantlycrystalline, and has a heat of fusion greater than 60 J/g or greaterthan 80 J/g.

[0253] The molecular weight of the polypropylene is not particularlylimited and can be, for example, from 10,000 to 5,000,000. Typically,the molecular weight will be from 50,000 to 500,000.

[0254] In some embodiments, the polypropylene has a polydispersity index(PDI) of from 1.5 to 40.

[0255] The polypropylene can be metallocene catalyzed or Ziegler-Nattacatalyzed.

[0256] mVLDPE-PP Blends

[0257] The mVLDPE/PP blends can be formed using conventional equipmentand methods, such a by dry blending the individual components andsubsequently melt mixing in a mixer, or by mixing the componentstogether directly in a mixer, such as a Banbury mixer, a Haake mixer, aBrabender internal mixer, or a single or twin-screw extruder including acompounding extruder and a side-arm extruder used directly downstream ofa polymerization process. Additionally, additives can be included in theblend, in one or more components of the blend, and/or in a productformed from the blend, as desired. Such additives are well known in theart, and can include, for example: fillers; antioxidants (e.g., hinderedphenolics such as IRGANOX™ 1010 or IRGANOX™ 1076 available fromCiba-Geigy); phosphites (e.g., IRGAFOS™ 168 available from Ciba-Geigy);UV stabilizers (e.g., hindered amine light stabilizer such as CHIMASORB™944 from Ciba Geigy); heat stabilizers; pigments; colorants; dyes; flameretardants (e.g., magnesium hydroxide, Zerogen™ 50 SP from J. M Huber);and the like.

[0258] A particularly desirable additive for roofing membraneapplications is a flame retardant. Flame retardants fall into two majorcategories: (1) additives that are simply compounded, mixed or dissolvedin the polymer substrate; and (2) additives that can be chemicallycoupled to the polymer, known as “reactive flame retardants.” Reactiveflame retardants are often used in thermoset polymer systems such aspolyesters, epoxies and polyurethane's.

[0259] When compounding plastics with flame retardants, considerationmust be given to how the flame retardant additives influence properties,as well as the compatibility with the host polymer. A flame retardantadditive cannot be volatile, or fugitive, that vaporizes before it canperform its intended function. The selection process for flameretardants includes considerations such as melt and vaporizationtemperatures, compatibility, and thermal decomposition temperature ofthe flame retardant. One skilled in the art can readily select theappropriate flame retardant or retardants.

[0260] Typical flame retardant formulations contain flame retardantadditives that can be classified as either halogenated ornon-halogenated. Halogenated flame retardants contain a mixture ofprimary, secondary or tertiary halogen, which can dehydrohalogenate overa wide range of temperatures. The evolution of the hydrogen halide isbeneficial to flame retardancy, but limits the maximum temperature atwhich the polymer compounds can be processed. Examples of halogencontaining flame retardants include chlorinated paraffins, andbrominated biphenyls such as tetrabromobisphenol A and decabromodiphenyloxide.

[0261] Non-halogenated flame retardants are mainly metallic oxides orhydroxides that contain water of hydration. The selection of inorganicflame retardant rests upon the ability of the flame retardant to retainwater under the polymer processing conditions. Examples of these includealuminum trihydride (ATH) and magnesium hydroxide, both of which providefire retardancy from their inherent water content. ATH tends to liberatewater at lower processing temperatures and is less useful forcompositions containing a higher melting polymer such as polypropylene.Magnesium hydroxide would be preferred for polypropylene-basedcompositions in view of its superior hydrolytic stability over a broadertemperature range. Antimony trioxide and zinc borate are also used asflame retardant additives in view of their fire retardancy. Antimonytrioxide is often used in combination with halogenated flame retardantadditives such as tetrabromobisphenol A.

[0262] Another family of flame retardants is the halogen and phosphoruscontaining compounds, such as tris(2,3-dibromopropyl)phosphate and otherphosphate esters. Antimony trioioxde is often used in combination withphosphate esters. These combinations are mainly applied in polyvinylchloride (PVC) and polystyrene formulations. In PVC compounds, theflammable plasticizers are replaced with phosphate and phosphate esteradditives.

[0263] Mixtures of flame retardants can also be used.

[0264] The blends include at least 10 weight percent and up to 90 weightpercent of the mVLDPE polymer, and at least 10 weight percent and up to90 weight percent of the polypropylene component, with these weightpercents based on the total weight of the mVLDPE and polypropylenecomponents of the blend. Alternative lower limits of the mVLDPE polymercan be 20%, 30%, 40% or 50% by weight. Alternative upper limits of themVLDPE polymer can be 80%, 70% or 60% by weight. Ranges from any lowerlimit to any upper limit are within the scope of the invention.

[0265] The mVLDPE polymer, the polypropylene polymer, or both, can beblends of such polymers. I.e., the mVLDPE polymer component of the blendcan itself be a blend of two or more VLDPE polymers having thecharacteristics described herein, and alternatively or additionally, thepolypropylene polymer component of the blend can itself be a blend oftwo or more polypropylene polymers, including the high rubber contentpolypropylene copolymers described above.

[0266] Other polymers can be included in the mVLDPE/PP blends ifdesired. Thus, in one embodiment, a mVLDPE/PP blend as described hereinfurther includes at least one ethylene alpha-olefin copolymer. Theethylene alpha-olefin copolymer can be a copolymer of ethylene and atleast one alpha-olefin, the alpha-olefin being any of the alpha-olefinsdescribed above in connection with the mVLDPE polymer, and especiallyC₃-C₁₀ alpha-olefins. Preferred ethylene-alpha olefins can have adensity of from a lower limit of 0.850 g/cm3 or 0.855 g/cm3 or 0.860g/cm3 or 0.862 g/cm3 to an upper limit of 0.905 g/cm3 or 0.902 g/cm3,with ranges from any lower limit to any upper limit. The ethylenealpha-olefin can be Ziegler-Natta catalyzed or metallocene catalyzed,and can have an alpha-olefin comonomer content sufficient to impart thedesired density. When present, the ethylene alpha-olefin comonomer canbe used in an amount of from 1 to 90% by weight, based on the weight ofthe mVLDPE/PP component, with alternative lower limits of 5 wt. % or 10wt. % or 20 wt. % or 30 wt. % or 40 wt. % and alternative upper limitsof 80 wt. % or 70 wt. % or 60 wt. % or 50 wt. %.

[0267] Membranes

[0268] Polymer blends of the present invention are particularly suitablefor applications such as for industrial roofing membranes, geomembranes,pond liners, and the like. Typical membranes have a thickness in therange of 0.1 to 10 mm, with a membranes of thickness 0.5 to 5 mm, or 1to 2 mm, being particularly common. The membranes can include one ormore layers of the polymer blends described herein, and optionally oneor more additional layers, such as reinforcing layers or scrim layers.Such membranes can be formed by any conventional means, such as byextrusion or calendering. In a typical method, the polymer blend iscompounded in an extruder with any desired additives, pelletized, andconverted to a flat membrane. Multi-layer membranes can be formed by anyconventional means of adhering such layers, such as forming one of thelayers separately in an extruder, and laminating the first layer with areinforcing scrim layer and a second layer in an extruder or acalendering process to form the composite.

[0269] It has been surprisingly found that membranes formed from polymerblends of the invention exhibit improved properties, particularlyimproved tensile strength and tear properties, relative to membranesformed of polypropylene/metallocene plastomer blends. As used herein,the term “plastomer” refers to ethylene/alpha-olefin copolymers having adensity ranging from 0.860 g/cm³ to 0.905 g/cm³ and alpha-olefin from C3to C20. Typical plastomers include EXACT™ plastomers available fromExxonMobil Chemical Co., Houston, Tex.

[0270] Membranes can also be composite structures; i.e., structuresincluding two or more layers. Thus, in one embodiment, the presentinvention is directed to composite structures having first and secondlayers formed of any of the mVLDPE/polypropylene blends describedherein, and an intermediate layer, such as an intermediate polymericreinforcing layer. Suitable intermediate layers can be, for example,polyester fabric, polypropylene fabric etc.

EXAMPLES Materials and Methods

[0271] Metallocene catalysts for the polymerization of the mVLDPE wereprepared according to the methods as described above for an unbridgedbis-Cp structure (such as bis (1,3-methyl-n-butyl cyclopentadienyl)zirconium dichloride).

[0272] Tensile strength values (tensile at yield, tensile at break,elongation at yield and elongation at break) were measured in accordancewith ASTM D412.

[0273] 100% Modulus was determined according to ASTM D412.

[0274] Tear Die C was determined according to ASTM D624.

[0275] The term “melt index” as used herein refers to the melt flow rateI_(2.16) at 190° C. according to ASTM D-1238, condition E. The term“MFR” as used herein refers to the melt flow rate I_(2.16) at 230° C.according to ASTM D-1238, condition L. This use of the terms “meltindex” and “MFR” is believed to be consistent with conventional usage inthe polyethylene and polypropylene fields, respectively.

[0276] Heat Weld Peel Strength was determined as follows. Samples of thecomposite membrane were cut into rectangular strips of 150 mm by 150 mm.Two of these composite structures were placed on top of each other witha 12 mm overlap. A strip of Mylar was placed on one edge of the assemblyto form a tab. The arrangement is such that the black bottom ply of thetop composite is in contact with the white top ply of the bottomcomposite. The two composite membranes were heat welded along theblack/white interface by using a hand held heat gun that can supply airat 700° F. (370° C.). A constant pressure from a 1-kg roller was appliedat the interface during heat welding. Strips of test specimens about 100mm long were cut from the edge containing the Mylar tab. The heat weldedcomposite was pulled apart at the tab in an Instron testing machineusing a cross head speed of 50 mm/min. The maximum force was recordedand converted to peel strength.

[0277] The ACD protocol is an analytical-scale TREF (Temperature RisingElution Fractionation) test for semi-crystalline copolymers tocharacterize the composition distribution (CD). A sample is dissolved ina good solvent, cooled slowly to allow crystallization on a support, andthen re-dissolved and washed from the support by heating during elution.Polymer chains are fractionated by differences in their crystallizationtemperature in solution, which is a function of composition (and defectstructure). A mass detector provides concentration vs. elutiontemperature data; CD characterization is obtained by applying acalibration curve (i.e., mole % comonomer vs. temperature) establishedusing narrow-CD standards. Two in-house Visual Basic programs are usedfor data acquisition and analysis.

[0278] There are really two distributions provided by the ACD test:

[0279] Solubility Distribution (weight fraction vs. solubilitytemperature)—measured directly.

[0280] Composition Distribution (weight fraction vs. comonomercontent)—obtained by applying the calibration curve to the solubilitydistribution.

[0281] Emphasis is usually placed on characterization of the CD.However, the solubility distribution can be of equal or greaterimportance when:

[0282] A calibration curve has not been established for the polymer ofinterest.

[0283] The MW of the sample is low, or the MWD is broad enough that asignificant portion of the sample is low MW (M<20k). Under thesecircumstances, the reported CD is influenced by the MW-dependence ofsolubility. The calibration curve must be corrected for the effect of MWto give the true CD, which requires a priori knowledge of the relativeinfluence of MW and composition on solubility for a given sample. Incontrast, the solubility distribution correctly accounts forcontributions from both effects, without trying to separate them.

[0284] Note that the solubility distribution should depend on solventtype and crystallization/dissolution conditions. If correctlycalibrated, the CD should be independent of changes in theseexperimental parameters.

[0285] Composition Distribution Breadth Index (CDBI) was measured usingthe following instrumentation: ACD: Modified Waters 150-C for TREF(Temperature Rising Elution Fractionation) analysis (includescrystallization column, by-pass plumbing, timing and temperaturecontrollers); Column: 75 micron glass bead packing in (High PressureLiquid Chromotography) HPLC-type column; Coolant: Liquid Nitrogen;Software: “A-TREF” Visual Basic programs; and Detector: PolymerLaboratories ELS-1000. Run conditions for the CDBI measurements were asfollows: GPC settings Mobile phase: TCE (tetrachlororethylene)Temperature: column compartment cycles 5-115° C., injector compartmentat 115° C. Run time:  1 hr 30 min Equilibration time:  10 min (beforeeach run) Flow rate:  2.5 mL/min Injection volume: 300 μL Pressuresettings: transducer adjusted to 0 when no flow, high pressure cut-offset to 30 bar

[0286] Temperature controller settings.

[0287] Initial Temperature: 115° C.

[0288] Ramp 1 Temperature: 5° C. Ramp time=45 min Dwell time=3 min

[0289] Ramp 2 Temperature: 115° C. Ramp time=30 min Dwell time=0 min

[0290] Alternative temperature controller settings if two peaks are notexhibited in a TREF measurement.

[0291] Initial Temperature: 115° C.

[0292] Ramp 1 Temperature: 5° C. Ramp time=12 hrs Dwell time=3 min

[0293] Ramp 2 Temperature: 115° C. Ramp time=12 hrs Dwell time=0 min

[0294] In some case, longer ramp times may be needed to show two peaksin a TREF measurement. ELS settings Nebulizer temperature: 120° C.Evaporator temperature: 135° C. Gas flow rate:  1.0 slm (standard litersper minute) Heated transfer line temperature: 120° C.

[0295] Melt Index was determined according to ASTM D-1238-95. Melt indexis reported in units of g/10 min, or the numerically equivalent units ofdg/min.

[0296] Density (g/cm³) was determined using chips cut from plaquescompression molded in accordance with ASTM D-1928-96 Procedure C, agedin accordance with ASTM D618 Procedure A, and measured according to ASTMD1505-96.

[0297] In the following Examples, resins produced by various supplierswere used to demonstrate the unique and advantageous properties of thepolymer blend compositions and membranes of the present invention. Itshould be understood that the specific numerical values of variousparameters of these resins described below are nominal values.

[0298] EXACT™ 0201 is an ethylene/octene plastomer made usingmetallocene catalyst, having a nominal density of 0.902 g/cm³ and a MeltIndex (I_(2.16), 190° C.) of 1.1 g/10 min, available from ExxonMobilChemical Co., Houston, Tex.

[0299] EXCEED™ ECD-321 is a gas-phase metallocene produced VLDPEethylene/hexene copolymer with a Melt Index (I_(2.16), 190° C.) of 1.0g/10 min, a density of 0.912 g/cm³, a melting point of 116.5° C., a CDBIof approximately 60-80%, and an MWD (Mw/Mn) of approximately 2.5-2.6,available from ExxonMobil Chemical Co., Houston, Tex.

[0300] ESCORENE™ 2232 is an isotactic polypropylene homopolymer havingan MFR (I_(2.16), 230° C.) of 3.0 g/10 min, available from ExxonMobilChemical Co., Houston, Tex.

[0301] ESCORENE™ 9272 is an istotactic polypropylene random copolymerhaving an MFR (I_(2.16), 230° C.) of 2.9 g/10 min, available fromExxonMobil Chemical Co., Houston, Tex.

[0302] ESCORENE™ 8102 is an isotactic polypropylene impact copolymerhaving an MFR (I_(2.16), 230° C.) of 1.9 g/10 min, available fromExxonMobil Chemical Co., Houston, Tex.

[0303] In the data tables following, the names of several commercialEXCEED™, EXACT™ and ESCORENE™ resins are abbreviated. Each occurrence ofthe abbreviated name should be interpreted as identifying a particularEXCEED™, EXACT™ or ESCORENE™ resin. EXCEED™, EXACT™ and ESCORENE™ aretrademarks of ExxonMobil Chemical Co., Houston, Tex.

Example 1

[0304] Producing mVLDPE

[0305] The EXCEED™ 321 mVLDPE polymer was prepared using gas phasepolymerization using metallocene catalyst systems as described above.The polymerizations were conducted in the continuous gas phase fluidizedbed reactors. The fluidized beds of those reactors were made up ofpolymer granules. The gaseous feed streams of ethylene and hydrogen wereintroduced below each reactor bed into the recycle gas line. Hexenecomonomer was introduced below the reactor bed. An inert hydrocarbon(isopentane) was also introduced to each reactor in the recycle gasline, to provide additional heat capacity to the reactor recycle gases.The individual flow rates of ethylene, hydrogen and hexene comonomerwere controlled to maintain fixed composition targets. The concentrationof the gases were measured by an on-line gas chromatograph to ensurerelatively constant composition in the recycle gas stream.

[0306] The solid catalyst was injected directly into the fluidized bedsusing purified nitrogen. The catalyst rates were adjusted to maintainconstant production rate. The reacting beds of growing polymer particleswere maintained in a fluidized state by a continuous flow of the make upfeed and recycle gas through each reaction zone. To maintain constantreactor temperatures, the temperature of the recycle gas wascontinuously adjusted up or down to accommodate any changes in the rateof heat generation due to the polymerization.

[0307] The fluidized bed was maintained at a constant height bywithdrawing a portion of the bed at a rate equal to the formation of theparticulate product. The product was transferred to a purger vessel toremove entrained hydrocarbons.

Example 2

[0308] White Ply Compound

[0309] White ply compounds were prepared, using magnesium hydroxide as aflame retardant, and a titanium dioxide pigment to impart the whitecolor. The compound also contained an antioxidant (IRGANOX™ 1010) and anultraviolet light stabilizer (CHIMASORB™ 944).

[0310] The white ply compound formulation is shown in Table 1. Theamounts shown in Table 1 are parts by weight rather than percentages.The mVLDPE and polypropylene components are specified generically;specific grades are shown in subsequent examples. TABLE 1 White PlyCompound Formulation Component Source Parts by Weight mVLDPE ExxonMobil60 Polypropylene ExxonMobil 16 Magnesium Hydroxide J. M. Huber 25(ZEROGEN ™ 50 SP) Titanium Dioxide Millenium Chemical 2.0 (TIONA ™RCL-6) Antioxidant Ciba Geigy 0.5 (IRGANOX ™ 1010) UV Stabilizer CibaGeigy 0.25 (CHIMASORB ™ 944)

[0311] Although Table 1 shows an exemplary formulation having specificamounts of various components, one skilled in the art will recognizethat the various amounts can be varied, based on the amounts of thepolymer components as described above, and the desired amounts of thevarious additives.

[0312] The compound of Table 1 was prepared using a two-step mixingprocess, as follows. To more effectively disperse the magnesiumhydroxide in the compound, a master batch containing 50 weight % of themVLDPE polymer and 50 weight % of the magnesium hydroxide was blended ina 7200 cm³ Banbury internal mixer. The polymer and magnesium hydroxidewere charged into the mixing chamber of the internal mixer with therotors running at 5 to 10 rpm. The mixing intensity was graduallyincreased until the polymer fluxed (melted) in the compound. Mixing wascontinued for an additional 2 minutes after the polymer flux. Thecompound was discharged from the internal mixer and ground into finepellets.

[0313] Next, the granulated magnesium hydroxide/mVLDPE master batch wascombined with the remaining components of Table 1, including additionalmVLDPE to achieve the noted amount, and the mixture was extruded using a30 mm ZSK twin screw extruder. The extruder zones varied in temperaturefrom 160° C. to 210° C. The compound was pelletized and compressionmolded into 20 mil (0.5 mm) thick pads, under conditions of 200° C. and8 minutes cycle time.

Example 3

[0314] Black Ply Compound

[0315] Black ply compounds were prepared using a blend of mVLDPE andpolypropylene, with a black concentrate and an antioxidant (IRGANOX™1010).

[0316] The black ply compound formulation is shown in Table 2. Theamounts shown in Table 2 are parts by weight rather than percentages.The mVLDPE and polypropylene components are specified generically;specific grades are shown in subsequent examples. TABLE 2 Black PlyCompound Formulation Component Source Parts by Weight mVLDPE ExxonMobil80 Polypropylene ExxonMobil 20 Antioxidant Ciba Geigy 0.5 (IRGANOX ™1010) Black Concentrate Ferro 0.1

[0317] Although Table 2 shows an exemplary formulation having specificamounts of various components, one skilled in the art will recognizethat the various amounts can be varied, based on the amounts of thepolymer components as described above, and the desired amounts of thevarious additives.

[0318] The compound of Table 2 was prepared in a single step processusing a 30 mm ZSK twin screw extruder. The extruder zones varied intemperature from 160° C. to 210° C. The compound was pelletized andcompression molded into 20 mil (0.5 mm) thick pads, under conditions of200° C. and 8 minutes cycle time.

Examples 4A and 4B

[0319] Blends with Polypropylene Homopolymer (HPP)

[0320] White and black plies were prepared as described in Examples 2and 3, using a polypropylene homopolymer as the polypropylene component,and several properties of the unreinforced plies were measured. Thepolypropylene homopolymer used was ESCORENE™ 2232.

[0321] In Example 4A, the compound included an mVLDPE, EXCEED™ 321, andthe polypropylene homopolymer. The properties of the white and blackplies are shown in Table 3.

[0322] Example 4B is a comparative example. In Example 4B, a metalloceneplastomer, EXACT™ 0201, was used in place of the mVLDPE. The propertiesof the plies are also shown in Table 3. TABLE 3 Properties ofUnreinforced Plies, Using PP Homopolymer (HPP) Example 4B Example 4A:m-plastomer/HPP mVLDPE/HPP (comparative) White Ply MFR (I_(2.16), 230°C.) (g/10 min) 1.4 1.8 100% Modulus (MPa) 13.4 9.8 Tensile at Yield(MPa) 14.1 10.4 Tensile at Break (MPa) 24.8 24.9 Elongation at Yield (%)40 50 Elongation at Break (%) 905 1495 Tear Die C (N/mm) 595 535 BlackPly MFR (I_(2.16), 230° C.) (g/10 min) 2.2 2.6 100% Modulus (MPa) 14.29.3 Tensile at Yield (MPa) 14.3 8.7 Tensile at Break (MPa) 42 32.7Elongation at Yield (%) 75 70 Elongation at Break (%) 900 2040 Tear DieC (N/mm) 595 542

[0323] As shown in Table 3, the inventive mVLDPE/polypropylenehomopolymer blends show superior tensile and tear properties in bothwhite ply and black ply compounds, compared to metallocene plastomercompounds of approximately the same MFR.

Examples 5A and 5B

[0324] Blends with Polypropylene Random Copolymer (RCP)

[0325] White and black plies were prepared as described in Examples 2and 3, using a polypropylene random copolymer as the polypropylenecomponent, and several properties of the unreinforced plies weremeasured. The polypropylene random copolymer used was ESCORENE™ 9272.

[0326] In Example 5A, the compound included an mVLDPE, EXCEED™ 321, andthe polypropylene random copolymer. The properties of the white andblack plies are shown in Table 4.

[0327] Example 5B is a comparative example. In Example 5B, a metalloceneplastomer, EXACT™ 0201, was used in place of the mVLDPE. The propertiesof the plies are also shown in Table 4. TABLE 4 Properties ofUnreinforced Plies, Using PP Random Copolymer (RCP) Example 5B Example5A: m-plastomer/RCP mVLDPE/RCP (comparative) White Ply MFR (I_(2.16),230° C.) (g/10 min) 1.6 1.7 100% Modulus (MPa) 12.8 8.8 Tensile at Yield(MPa) 13.7 9.2 Tensile at Break (MPa) 23.4 23.2 Elongation at Yield (%)50 60 Elongation at Break (%) 930 1525 Tear Die C (N/mm) 595 450 BlackPly MFR (I_(2.16), 230° C.) (g/10 min) 2.2 2.4 100% Modulus (MPa) 12.29.0 Tensile at Yield (MPa) 12.5 8.9 Tensile at Break (MPa) 39.8 25.3Elongation at Yield (%) 75 85 Elongation at Break (%) 930 1695 Tear DieC (N/mm) 515 510

[0328] As shown in Table 4, the inventive mVLDPE/polypropylene randomcopolymer blends show superior tensile and tear properties in both whiteply and black ply compounds, compared to metallocene plastomer compoundsof approximately the same MFR.

Examples 6A and 6B

[0329] Blends with Polypropylene Impact Copolymer (ICP)

[0330] White and black plies were prepared as described in Examples 2and 3, using a polypropylene impact copolymer as the polypropylenecomponent, and several properties of the unreinforced plies weremeasured. The polypropylene impact copolymer used was ESCORENE™ 8102.

[0331] In Example 6A, the compound included an mVLDPE, EXCEED™ 321, andthe polypropylene impact copolymer. The properties of the white andblack plies are shown in Table 5.

[0332] Example 6B is a comparative example. In Example 6B, a metalloceneplastomer, EXACT™ 0201, was used in place of the mVLDPE. The propertiesof the plies are also shown in Table 5. TABLE 5 Properties ofUnreinforced Plies, Using PP Impact Copolymer (ICP) Example 6B Example6A: m-plastomer/ICP mVLDPE/ICP (comparative) White Ply MFR (I2.16, 230°C.) (g/10 min) 1.6 1.6 100% Modulus (MPa) 11.3 6.9 Tensile at Yield(MPa) 11.6 7.5 Tensile at Break (MPa) 20.5 20.7 Elongation at Yield (%)45 45 Elongation at Break (%) 900 1785 Tear Die C (N/mm) 535 415 BlackPly MFR (I2.16, 230° C.) (g/10 min) 2.2 2.4 100% Modulus (MPa) 9.3 7.1Tensile at Yield (MPa) 9.4 6.9 Tensile at Break (MPa) 33.0 27.2Elongation at Yield (%) 75 60 Elongation at Break (%) 900 2050 Tear DieC (N/mm) (no data) 450

[0333] As shown in Table 5, the inventive mVLDPE/polypropylenehomopolymer blends show superior tensile and tear properties in thewhite ply compound, and superior tensile properties in the black plycompound, compared to metallocene plastomer compounds of approximatelythe same MFR.

Example 7

[0334] Scrim Reinforced Composite Membranes

[0335] Composite membranes were formed by combining a white top plyaccording to Example 2 and a corresponding black bottom ply according toExample 3, with 1 mil (25 μm) thick polyester scrim fabric between thewhite and black plies. The polyester scrim fabric was obtained fromHighland Industries. The composite assembly was then compression moldedin a 43 mil (1.1 mm) mold cavity at 200° C. for 8 minutes.

[0336] Properties of reinforced membranes are shown in the followingexamples. One skilled in the art will appreciate that the enhancedtensile and tear properties of membranes of the present invention aremore readily apparent in the unreinforced membrane properties describedabove.

Examples 8A and 8B

[0337] Composite Membranes with Polypropylene Homopolymer (HPP)

[0338] Composite membranes were formed according to Example 7, using thewhite and black plies of Examples 4A and 4B. Example 8B is a comparativeexample. The properties of the scrim-reinforced composite membranes areshown in Table 6. TABLE 6 Properties of Reinforced Composite MembranesUsing PP Homopolymer (HPP) Example 8B Example 8A: m-plastomer/HPPmVLDPE/HPP (comparative) Tensile at Yield (MPa) 33.6 30.1 Elongation atBreak (%) 57 170 Heat Weld Peel Strength (N/mm) 120 130

[0339] Examples 9A and 9B

[0340] Composite Membranes with Polypropylene Random Copolymer (RCP)

[0341] Composite membranes were formed according to Example 7, using thewhite and black plies of Examples 5A and 5B. Example 9B is a comparativeexample. The properties of the scrim-reinforced composite membranes areshown in Table 7. TABLE 7 Properties of Reinforced Composite MembranesUsing PP Random Copolymer (RCP) Example 9B Example 9A: m-plastomer/HPPmVLDPE/HPP (comparative) Tensile at Yield (MPa) 28.1 28.2 Elongation atBreak (%) 63 75 Heat Weld Peel Strength (N/mm) 92 135

Examples 10A and 10B

[0342] Composite Membranes with Polypropylene Impact Copolymer (ICP)

[0343] Composite membranes were formed according to Example 7, using thewhite and black plies of Examples 6A and 6B. Example 10B is acomparative example. The properties of the scrim-reinforced compositemembranes are shown in Table 8. TABLE 8 Properties of ReinforcedComposite Membranes Using PP Impact Copolymer (ICP) Example 10B Example10A: m-plastomer/ICP mVLDPE/ICP (comparative) Tensile at Yield (MPa)28.5 28.9 Elongation at Break (%) 180 57 Heat Weld Peel Strength (N/mm)184 148

[0344] Various tradenames used herein are indicated by a ™ symbol,indicating that the names may be protected by certain trademark rights.Some such names may also be registered trademarks in variousjurisdictions.

[0345] All patents, test procedures, and other documents cited herein,including priority documents, are fully incorporated by reference to theextent such disclosure is not inconsistent with this invention and forall jurisdictions in which such incorporation is permitted.

What is claimed is:
 1. A membrane formed from a polymer blendcomposition comprising: (a) a metallocene-catalyzed VLDPE copolymer ofethylene and one or more C₃-C₂₀ alpha olefin comonomers, the copolymerhaving a density of from 0.906 g/cm³ to 0.915 g/cm³, and (b) apolypropylene polymer component, wherein components (a) and (b) arepresent in the blend composition in a weight ratio of from 9:1 to 1:9.2. The membrane of claim 1, wherein the propylene polymer componentcomprises polypropylene selected from: propylene homopolymers; randomcopolymers of propylene and one or more comonomers selected fromethylene and C₃-C₂₀ alpha olefins; impact copolymers of propylene andone or more comonomers selected from ethylene and C₃-C₂₀ alpha olefins;high rubber content polypropylenes; and mixtures thereof.
 3. Themembrane of claim 1, wherein the propylene polymer component comprisespolypropylene selected from: propylene homopolymers; random copolymersof propylene and ethylene; impact copolymers of propylene and ethylene;reactor alloys of ethylene-propylene rubber and crystallinepolypropylene; and mixtures thereof.
 4. The membrane of claim 1, whereinthe polypropylene polymer component comprises polypropylene/ethylenecopolymer having a polymerized ethylene content of from 0.5 to 40 wt. %.5. The membrane of claim 1, wherein the polypropylene polymer componentcomprises polypropylene/ethylene random copolymer having a polymerizedethylene content of from 1 to 10 wt. %.
 6. The membrane of claim 1,wherein the polypropylene polymer component comprisespolypropylene/ethylene impact copolymer having an overall polymerizedethylene content of from 1 to 15 wt. %.
 7. The membrane of claim 1,wherein the weight ratio of component (a) to component (b) is from 9:1to 1:1.
 8. The membrane of claim 1, wherein the metallocene catalyzedVLDPE copolymer is produced using an unbridged bis-Cp metallocenecatalyst system.
 9. The membrane of claim 1, wherein the metallocenecatalyzed VLDPE copolymer has: (i) a comonomer content of from 5 to 15wt. %, (ii) a composition distribution breadth index of from 50% to 85%,(iii) a molecular weight distribution Mw/Mn of from 2 to 3, (iv) amolecular weight distribution Mz/Mw of less than 2, and (v) a bimodalcomposition distribution.
 10. The membrane of claim 1, wherein thepolymer blend composition further comprises (c) at least one ethylene,alpha-olefin copolymer in an amount such that the weight ratio of (c) tothe sum of (a) and (b) is from 0.1:9 9:1.
 11. The membrane of claim 10,wherein the at least one ethylene alpha-olefin copolymer has a densityof from 0.850 g/cm³ to 0.905 g/cm³ and is selected frommetallocene-catalyzed copolymers of ethylene and at least one C₃ to C₁₀alpha-olefin, Ziegler-Natta catalyzed copolymers of ethylene and atleast one C₃ to C₁₀ alpha-olefin, and mixtures thereof.
 12. The membraneof claim 1, wherein the polymer blend further comprises a flameretardant in an amount of 1 to 50 wt. %, based on the total weight ofthe polymer blend composition.
 13. A membrane formed from a polymerblend composition comprising: (a) a metallocene-catalyzed VLDPEcopolymer of ethylene and one or more C₃-C₁₂ alpha olefin comonomers,the copolymer having a density of from 0.906 g/cm³ to 0.915 g/cm³, and(b) a polypropylene polymer component comprising at least one of apolypropylene homopolymer and a polypropylene/ethylene copolymer havinga polymerized ethylene content of from 0.5 to 40 wt. %, whereincomponents (a) and (b) are present in the blend composition in a weightratio of from 9:1 to 1:1.
 14. The membrane of claim 13, wherein thepropylene polymer component comprises polypropylene selected from:propylene homopolymers; random copolymers of propylene ethylene; impactcopolymers of propylene and ethylene; reactor alloys ofethylene-propylene rubber and crystalline polypropylene; and mixturesthereof.
 15. The membrane of claim 13, wherein the polypropylene polymercomponent comprises polypropylene/ethylene random copolymer having apolymerized ethylene content of from 1 to 10 wt. %.
 16. The membrane ofclaim 13, wherein the polypropylene polymer component comprisespolypropylene/ethylene impact copolymer having an overall polymerizedethylene content of from 1 to 15 wt. %.
 17. The membrane of claim 13,wherein the metallocene catalyzed VLDPE copolymer is produced using anunbridged bis-Cp metallocene catalyst system.
 18. The membrane of claim13, wherein the metallocene catalyzed VLDPE copolymer has: (i) acomonomer content of from 5 to 15 wt. %, (ii) a composition distributionbreadth index of from 50% to 85%, (iii) a molecular weight distributionMw/Mn of from 2 to 3, (iv) a molecular weight distribution Mz/Mw of lessthan 2, and (v) a bimodal composition distribution.
 19. The membrane ofclaim 13, wherein the polymer blend composition further comprises (c) atleast one ethylene, alpha-olefin copolymer in an amount such that theweight ratio of (c) to the sum of (a) and (b) is from 0.1:9 9:1.
 20. Themembrane of claim 19, wherein the at least one ethylene alpha-olefincopolymer has a density of from 0.850 g/cm³ to 0.905 g/cm³ and isselected from metallocene-catalyzed copolymers of ethylene and at leastone C₃ to C₁₀ alpha-olefin, Ziegler-Natta catalyzed copolymers ofethylene and at least one C₃ to C₁₀ alpha-olefin, and mixtures thereof.21. The membrane of claim 13, wherein the polymer blend furthercomprises a flame retardant in an amount of 1 to 50 wt. %, based on thetotal weight of the polymer blend composition.
 22. A composite membranecomprising first and second layers, and an intermediate polymericreinforcing layer disposed between the first and second layers, whereinthe first and second layers are the same or different and are formedfrom a polymer blend composition comprising: (a) a metallocene-catalyzedVLDPE copolymer of ethylene and one or more C₃-C₂₀ alpha olefincomonomers, the copolymer having a density of from 0.906 g/cm³ to 0.915g/cm³, and (b) a polypropylene polymer component, wherein components (a)and (b) are present in the blend composition in a weight ratio of from9:1 to 1:9.
 23. The composite membrane of claim 22, wherein thepropylene polymer component comprises polypropylene selected from:propylene homopolymers; random copolymers of propylene and one or morecomonomers selected from ethylene and C₃-C₂₀ alpha olefins; impactcopolymers of propylene and one or more comonomers selected fromethylene and C₃-C₂₀ alpha olefins; high rubber content polypropylenes;and mixtures thereof.
 24. The composite membrane of claim 22, whereinthe propylene polymer component comprises polypropylene selected from:propylene homopolymers; random copolymers of propylene and ethylene;impact copolymers of propylene and ethylene; reactor alloys ofethylene-propylene rubber and crystalline polypropylene; and mixturesthereof.
 25. The composite membrane of claim 22, wherein thepolypropylene polymer component comprises polypropylene/ethylenecopolymer having a polymerized ethylene content of from 0.5 to 40 wt. %.26. The membrane of claim 22, wherein the polypropylene polymercomponent comprises polypropylene/ethylene random copolymer having apolymerized ethylene content of from 1 to 10 wt. %.
 27. The compositemembrane of claim 22, wherein the polypropylene polymer componentcomprises polypropylene/ethylene impact copolymer having a polymerizedethylene content of from 1 to 15 wt. %.
 28. The membrane of claim 22,wherein the weight ratio of component (a) to component (b) is from 9:1to 1:1.
 29. The membrane of claim 23, wherein the metallocene catalyzedVLDPE copolymer is produced using an unbridged bis-Cp metallocenecatalyst system.
 30. The membrane of claim 22, wherein the metallocenecatalyzed VLDPE copolymer has: (i) a comonomer content of from 5 to 15wt. %, (ii) a composition distribution breadth index of from 50% to 85%,(iii) a molecular weight distribution Mw/Mn of from 2 to 3, (iv) amolecular weight distribution Mz/Mw of less than 2, and (v) a bimodalcomposition distribution.
 31. The membrane of claim 22, wherein thepolymer blend composition further comprises (c) at least one ethylene,alpha-olefin copolymer in an amount such that the weight ratio of (c) tothe sum of (a) and (b) is from 0.1:9 9:1.
 32. The membrane of claim 31,wherein the at least one ethylene alpha-olefin copolymer has a densityof from 0.850 g/cm³ to 0.905 g/cm³ and is selected frommetallocene-catalyzed copolymers of ethylene and at least one C₃ to C₁₀alpha-olefin, Ziegler-Natta catalyzed copolymers of ethylene and atleast one C₃ to C₁₀ alpha-olefin, and mixtures thereof.
 33. The membraneof claim 22, wherein the polymer blend further comprises a flameretardant in an amount of 1 to 50 wt. %, based on the total weight ofthe polymer blend composition.
 34. A membrane formed from a polymerblend composition comprising: (a) a copolymer of ethylene and one ormore C₃-C₂₀ alpha olefin comonomers, the copolymer having: (i) acomonomer content of from 5 to 15 wt. %, (ii) a density of less than0.916 g/cm³, (iii) a composition distribution breadth index of from 50%to 85%, (iv) a molecular weight distribution Mw/Mn of from 2 to 3, (v) amolecular weight distribution Mz/Mw of less than 2, and (vi) a bimodalcomposition distribution; and (b) a polypropylene polymer component,wherein components (a) and (b) are present in the blend composition in aweight ratio of 9:1 to 1:9
 35. The membrane of claim 34, wherein thepropylene polymer component comprises polypropylene selected from:propylene homopolymers; random copolymers of propylene and one or morecomonomers selected from ethylene and C₃-C₂₀ alpha olefins; impactcopolymers of propylene and one or more comonomers selected fromethylene and C₃-C₂₀ alpha olefins; high rubber content polypropylenes;and mixtures thereof.
 36. The membrane of claim 34, wherein thepropylene polymer component comprises polypropylene selected from:propylene homopolymers; random copolymers of propylene and ethylene;impact copolymers of propylene and ethylene; reactor alloys ofethylene-propylene rubber and crystalline polypropylene; and mixturesthereof.
 37. The membrane of claim 34, wherein the polypropylene polymercomponent comprises polypropylene/ethylene copolymer having apolymerized ethylene content of from 0.5 to 40 wt. %.
 38. The membraneof claim 34, wherein the polypropylene polymer component comprisespolypropylene/ethylene random copolymer having a polymerized ethylenecontent of from 1 to 10 wt. %.
 39. The membrane of claim 34, wherein thepolypropylene polymer component comprises polypropylene/ethylene impactcopolymer having a polymerized ethylene content of from 1 to 15 wt. %.40. The membrane of claim 34, wherein the weight ratio of component (a)to component (b) is from 9:1 to 1:1.
 41. The membrane of claim 34,wherein the metallocene catalyzed VLDPE copolymer is produced using anunbridged bis-Cp metallocene catalyst system.
 42. The membrane of claim34, wherein the polymer blend composition further comprises (c) at leastone ethylene, alpha-olefin copolymer in an amount such that the weightratio of (c) to the sum of (a) and (b) is from 0.1:9 9:1.
 43. Themembrane of claim 42, wherein the at least one ethylene alpha-olefincopolymer has a density of from 0.850 g/cm³ to 0.905 g/cm³ and isselected from metallocene-catalyzed copolymers of ethylene and at leastone C₃ to C₁₀ alpha-olefin, Ziegler-Natta catalyzed copolymers ofethylene and at least one C₃ to C₁₀ alpha-olefin, and mixtures thereof.44. The membrane of claim 34, wherein the polymer blend furthercomprises a flame retardant in an amount of 1 to 50 wt. %, based on thetotal weight of the polymer blend composition.
 45. A composite membranecomprising first and second layers, and an intermediate polymericreinforcing layer disposed between the first and second layers, whereinthe first and second layers are the same or different and are formedfrom a polymer blend composition comprising: (a) a metallocene-catalyzedVLDPE copolymer of ethylene and one or more C₃-C₂₀ alpha olefincomonomers, the copolymer having: (i) a comonomer content of from 5 to15 wt. %, (ii) a density of less than 0.916 g/cm³, (iii) a compositiondistribution breadth index of from 50% to 85%, (iv) a molecular weightdistribution Mw/Mn of from 2 to 3, (v) a molecular weight distributionMz/Mw of less than 2, and (vi) a bimodal composition distribution; and(b) a polypropylene polymer component, wherein components (a) and (b)are present in the blend composition in a weight ratio of from 9:1 to1:9.
 46. The composite membrane of claim 45, wherein the propylenepolymer component comprises polypropylene selected from: propylenehomopolymers; random copolymers of propylene and one or more comonomersselected from ethylene and C₃-C₂₀ alpha olefins; impact copolymers ofpropylene and one or more comonomers selected from ethylene and C₃-C₂₀alpha olefins; high rubber content polypropylenes; and mixtures thereof.47. The composite membrane of claim 45, wherein the propylene polymercomponent comprises polypropylene selected from: propylene homopolymers;random copolymers of propylene and ethylene; impact copolymers ofpropylene and ethylene; reactor alloys of ethylene-propylene rubber andcrystalline polypropylene; and mixtures thereof.
 48. The compositemembrane of claim 45, wherein the polypropylene polymer componentcomprises polypropylene/ethylene copolymer having a polymerized ethylenecontent of from 0.5 to 40 wt. %.
 49. The membrane of claim 45, whereinthe polypropylene polymer component comprises polypropylene/ethylenerandom copolymer having a polymerized ethylene content of from 1 to 10wt. %.
 50. The composite membrane of claim 45, wherein the polypropylenepolymer component comprises polypropylene/ethylene impact copolymerhaving a polymerized ethylene content of from 1 to 15 wt. %.
 51. Themembrane of claim 45, wherein the weight ratio of component (a) tocomponent (b) is from 9:1 to 1:1.
 52. The membrane of claim 45, whereinthe metallocene catalyzed VLDPE copolymer is produced using an unbridgedbis-Cp metallocene catalyst system.
 53. The membrane of claim 45,wherein the polymer blend composition further comprises (c) at least oneethylene, alpha-olefin copolymer in an amount such that the weight ratioof (c) to the sum of (a) and (b) is from 0.1:9 9:1.
 54. The membrane ofclaim 53, wherein the at least one ethylene alpha-olefin copolymer has adensity of from 0.850 g/cm³ to 0.905 g/cm³ and is selected frommetallocene-catalyzed copolymers of ethylene and at least one C₃ to C₁₀alpha-olefin, Ziegler-Natta catalyzed copolymers of ethylene and atleast one C₃ to C₁₀ alpha-olefin, and mixtures thereof.
 55. The membraneof claim 45, wherein the polymer blend further comprises a flameretardant in an amount of 1 to 50 wt. %, based on the total weight ofthe polymer blend composition.